diff --git a/protoveneer/README.md b/protoveneer/README.md
new file mode 100644
index 0000000..95283c7
--- /dev/null
+++ b/protoveneer/README.md
@@ -0,0 +1,5 @@
+# The protoveneer tool
+
+Protoveneer is an experimental tool that generates idiomatic Go types that
+correspond to protocol buffer messages and enums -- a veneer on top of the proto
+layer.
diff --git a/protoveneer/cmd/protoveneer/config.go b/protoveneer/cmd/protoveneer/config.go
new file mode 100644
index 0000000..0907df0
--- /dev/null
+++ b/protoveneer/cmd/protoveneer/config.go
@@ -0,0 +1,98 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"errors"
+	"fmt"
+	"os"
+
+	"gopkg.in/yaml.v3"
+)
+
+// config holds the configuration for a package.
+type config struct {
+	Package         string
+	ProtoImportPath string `yaml:"protoImportPath"`
+	// Import path for the support package needed by the generated code.
+	SupportImportPath string `yaml:"supportImportPath"`
+
+	// The types to process. Only these types and the types they depend
+	// on will be output.
+	// The key is the name of the proto type.
+	Types map[string]*typeConfig
+	// Omit the types in this list, even if they would normally be output.
+	// Elements can be globs.
+	OmitTypes []string `yaml:"omitTypes"`
+	// Converter functions for types not in the proto package.
+	// Each value should be "tofunc, fromfunc"
+	Converters map[string]string
+}
+
+type typeConfig struct {
+	// The name for the veneer type, if different.
+	Name string
+	// The prefix of the proto enum values. It will be removed.
+	ProtoPrefix string `yaml:"protoPrefix"`
+	// The prefix for the veneer enum values, if different from the type name.
+	VeneerPrefix string `yaml:"veneerPrefix"`
+	// Overrides for enum values.
+	ValueNames map[string]string `yaml:"valueNames"`
+	// Overrides for field types. Map key is proto field name.
+	Fields map[string]fieldConfig
+	// Custom conversion functions: "tofunc, fromfunc"
+	ConvertToFrom string `yaml:"convertToFrom"`
+	// Doc string for the type, omitting the initial type name.
+	Doc string
+	// Verb to place after type name in doc. Default: "is".
+	// Ignored if Doc is non-empty.
+	DocVerb string `yaml:"docVerb"`
+}
+
+type fieldConfig struct {
+	Name string // veneer name
+	Type string // veneer type
+	// Omit from output.
+	Omit bool
+}
+
+func (c *config) init() {
+	for protoName, tc := range c.Types {
+		if tc == nil {
+			tc = &typeConfig{Name: protoName}
+			c.Types[protoName] = tc
+		}
+		if tc.Name == "" {
+			tc.Name = protoName
+		}
+		tc.init()
+	}
+}
+
+func (tc *typeConfig) init() {
+	if tc.VeneerPrefix == "" {
+		tc.VeneerPrefix = tc.Name
+	}
+}
+
+func readConfigFile(filename string) (*config, error) {
+	if filename == "" {
+		return nil, errors.New("missing config file")
+	}
+	f, err := os.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	dec := yaml.NewDecoder(f)
+	dec.KnownFields(true)
+
+	var c config
+	if err := dec.Decode(&c); err != nil {
+		return nil, fmt.Errorf("reading %s: %w", filename, err)
+	}
+	c.init()
+	return &c, nil
+}
diff --git a/protoveneer/cmd/protoveneer/converters.go b/protoveneer/cmd/protoveneer/converters.go
new file mode 100644
index 0000000..a9afd70
--- /dev/null
+++ b/protoveneer/cmd/protoveneer/converters.go
@@ -0,0 +1,143 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "fmt"
+
+// A converter generates code to convert between a proto type and a veneer type.
+type converter interface {
+	// genFrom returns code to convert from proto to veneer.
+	genFrom(string) string
+	// genTo returns code to convert to proto from veneer.
+	genTo(string) string
+	// These return the function argument to Transform{Slice,MapValues}, or "" if we don't need it.
+	genTransformFrom() string
+	genTransformTo() string
+}
+
+// An identityConverter does no conversion.
+type identityConverter struct{}
+
+func (identityConverter) genFrom(arg string) string { return arg }
+func (identityConverter) genTo(arg string) string   { return arg }
+func (identityConverter) genTransformFrom() string  { return "" }
+func (identityConverter) genTransformTo() string    { return "" }
+
+// A derefConverter converts between T in the veneer and *T in the proto.
+type derefConverter struct{}
+
+func (derefConverter) genFrom(arg string) string { return fmt.Sprintf("support.DerefOrZero(%s)", arg) }
+func (derefConverter) genTo(arg string) string   { return fmt.Sprintf("support.AddrOrNil(%s)", arg) }
+func (derefConverter) genTransformFrom() string  { panic("can't handle deref slices") }
+func (derefConverter) genTransformTo() string    { panic("can't handle deref slices") }
+
+type enumConverter struct {
+	protoName, veneerName string
+}
+
+func (c enumConverter) genFrom(arg string) string {
+	return fmt.Sprintf("%s(%s)", c.veneerName, arg)
+}
+
+func (c enumConverter) genTransformFrom() string {
+	return fmt.Sprintf("func(p pb.%s) %s { return %s }", c.protoName, c.veneerName, c.genFrom("p"))
+}
+
+func (c enumConverter) genTo(arg string) string {
+	return fmt.Sprintf("pb.%s(%s)", c.protoName, arg)
+}
+
+func (c enumConverter) genTransformTo() string {
+	return fmt.Sprintf("func(v %s) pb.%s { return %s }", c.veneerName, c.protoName, c.genTo("v"))
+}
+
+type protoConverter struct {
+	veneerName string
+}
+
+func (c protoConverter) genFrom(arg string) string {
+	return fmt.Sprintf("(%s{}).fromProto(%s)", c.veneerName, arg)
+}
+
+func (c protoConverter) genTransformFrom() string {
+	return fmt.Sprintf("(%s{}).fromProto", c.veneerName)
+}
+
+func (c protoConverter) genTo(arg string) string {
+	return fmt.Sprintf("%s.toProto()", arg)
+}
+
+func (c protoConverter) genTransformTo() string {
+	return fmt.Sprintf("(*%s).toProto", c.veneerName)
+}
+
+type customConverter struct {
+	toFunc, fromFunc string
+}
+
+func (c customConverter) genFrom(arg string) string {
+	return fmt.Sprintf("%s(%s)", c.fromFunc, arg)
+}
+
+func (c customConverter) genTransformFrom() string { return c.fromFunc }
+
+func (c customConverter) genTo(arg string) string {
+	return fmt.Sprintf("%s(%s)", c.toFunc, arg)
+}
+
+func (c customConverter) genTransformTo() string { return c.toFunc }
+
+type sliceConverter struct {
+	eltConverter converter
+}
+
+func (c sliceConverter) genFrom(arg string) string {
+	if fn := c.eltConverter.genTransformFrom(); fn != "" {
+		return fmt.Sprintf("support.TransformSlice(%s, %s)", arg, fn)
+	}
+	return c.eltConverter.genFrom(arg)
+}
+
+func (c sliceConverter) genTo(arg string) string {
+	if fn := c.eltConverter.genTransformTo(); fn != "" {
+		return fmt.Sprintf("support.TransformSlice(%s, %s)", arg, fn)
+	}
+	return c.eltConverter.genTo(arg)
+}
+
+func (c sliceConverter) genTransformTo() string {
+	panic("sliceConverter.genToSlice called")
+}
+
+func (c sliceConverter) genTransformFrom() string {
+	panic("sliceConverter.genFromSlice called")
+}
+
+// Only the values are converted.
+type mapConverter struct {
+	valueConverter converter
+}
+
+func (c mapConverter) genFrom(arg string) string {
+	if fn := c.valueConverter.genTransformFrom(); fn != "" {
+		return fmt.Sprintf("support.TransformMapValues(%s, %s)", arg, fn)
+	}
+	return c.valueConverter.genFrom(arg)
+}
+
+func (c mapConverter) genTo(arg string) string {
+	if fn := c.valueConverter.genTransformTo(); fn != "" {
+		return fmt.Sprintf("support.TransformMapValues(%s, %s)", arg, fn)
+	}
+	return c.valueConverter.genTo(arg)
+}
+
+func (c mapConverter) genTransformTo() string {
+	panic("mapConverter.genToSlice called")
+}
+
+func (c mapConverter) genTransformFrom() string {
+	panic("mapConverter.genFromSlice called")
+}
diff --git a/protoveneer/cmd/protoveneer/protoveneer.go b/protoveneer/cmd/protoveneer/protoveneer.go
new file mode 100644
index 0000000..bfe36ce
--- /dev/null
+++ b/protoveneer/cmd/protoveneer/protoveneer.go
@@ -0,0 +1,856 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// protoveneer generates idiomatic Go types that correspond to protocol
+// buffer messages and enums -- a veneer on top of the proto layer.
+//
+// # Relationship to GAPICs
+//
+// GAPICs and this tool complement each other.
+//
+// GAPICs have client types and idiomatic methods on them that correspond to
+// RPCs. They focus on the RPC part of a service. A GAPIC relies on the
+// underlying protocol buffer types for the request and response types, and all
+// the types that these refer to.
+//
+// protoveener generates Go types that correspond to proto messages and enums,
+// including requests and responses if desired. It doesn't touch the RPC parts
+// of the proto definition.
+//
+// # Configuration
+//
+// protoveneer requires significant configuration to produce good results.
+// See the config type in config.go and the config.yaml files in the testdata
+// subdirectories to understand how to write configuration.
+//
+// # Support functions
+//
+// protoveneer generates code that relies on a few support functions. These live
+// in the support subdirectory. You should copy the contents of this directory
+// to a location of your choice, and add "supportImportPath" to your config to
+// refer to that directory's import path.
+//
+// # Unhandled features
+//
+// There is no support for oneofs. Omit the oneof type and write custom code.
+// However, the types of the individual oneof cases can be generated.
+package main
+
+// TODO:
+// - have omitFields on a TypeConfig, like omitTypes
+// - Instead of parseCustomConverter, accept a list. Users can use the inline form
+//   to be compact.
+// - Check that a configured field is actually in the type.
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"go/ast"
+	"go/format"
+	"go/parser"
+	"go/token"
+	"io"
+	"log"
+	"os"
+	"path"
+	"path/filepath"
+	"sort"
+	"strings"
+	"text/template"
+	"time"
+	"unicode"
+)
+
+var (
+	outputDir = flag.String("outdir", "", "directory to write to, or '-' for stdout")
+	noFormat  = flag.Bool("nofmt", false, "do not format output")
+)
+
+func main() {
+	log.SetPrefix("protoveneer: ")
+	log.SetFlags(0)
+	flag.Usage = func() {
+		out := flag.CommandLine.Output()
+		fmt.Fprintf(out, "usage: protoveneer CONFIG.yaml DIR_WITH_pb.go_FILES\n")
+		flag.PrintDefaults()
+	}
+	flag.Parse()
+
+	if err := run(context.Background(), flag.Arg(0), flag.Arg(1), *outputDir); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func run(ctx context.Context, configFile, pbDir, outDir string) error {
+	config, err := readConfigFile(configFile)
+	if err != nil {
+		return err
+	}
+
+	fset := token.NewFileSet()
+	pkg, err := parseDir(fset, pbDir)
+	if err != nil {
+		return err
+	}
+
+	src, err := generate(config, pkg, fset)
+	if err != nil {
+		return err
+	}
+	if !*noFormat {
+		src, err = format.Source(src)
+		if err != nil {
+			return err
+		}
+	}
+
+	if outDir == "-" {
+		fmt.Printf("%s\n", src)
+	} else {
+		outfile := fmt.Sprintf("%s_veneer.gen.go", pkg.Name)
+		if outDir != "" {
+			outfile = filepath.Join(outDir, outfile)
+		}
+		if err := os.WriteFile(outfile, src, 0660); err != nil {
+			log.Fatal(err)
+		}
+		fmt.Printf("wrote %s\n", outfile)
+	}
+	return nil
+}
+
+func parseDir(fset *token.FileSet, dir string) (*ast.Package, error) {
+	pkgs, err := parser.ParseDir(fset, dir, nil, parser.ParseComments)
+	if err != nil {
+		return nil, err
+	}
+	if len(pkgs) > 2 {
+		return nil, errors.New("too many packages")
+	}
+	var pkg *ast.Package
+	for name, apkg := range pkgs {
+		if !strings.HasSuffix(name, "_test") {
+			pkg = apkg
+			break
+		}
+	}
+	if pkg == nil {
+		return nil, errors.New("no non-test package")
+	}
+	for filename := range pkg.Files {
+		if !strings.HasSuffix(filename, ".pb.go") {
+			return nil, fmt.Errorf("%s is not a .pb.go file", filename)
+		}
+	}
+	return pkg, nil
+}
+
+func generate(conf *config, pkg *ast.Package, fset *token.FileSet) (src []byte, err error) {
+	// Get information about all the types in the proto package.
+	typeInfos, err := collectDecls(pkg)
+	if err != nil {
+		return nil, err
+	}
+
+	// Check that every configured type is present.
+	for protoName := range conf.Types {
+		if typeInfos[protoName] == nil {
+			return nil, fmt.Errorf("configured type %s does not exist in package", protoName)
+		}
+	}
+
+	// Consult the config to determine which types to omit.
+	// If a type isn't matched by a glob in the OmitTypes list, it is output.
+	// If a type is matched, but it also has a config, it is still output.
+	var toWrite []*typeInfo
+	for name, ti := range typeInfos {
+		if !ast.IsExported(name) {
+			continue
+		}
+		omit, err := sliceAnyError(conf.OmitTypes, func(glob string) (bool, error) {
+			return path.Match(glob, name)
+		})
+		if err != nil {
+			return nil, err
+		}
+		if !omit || conf.Types[name] != nil {
+			toWrite = append(toWrite, ti)
+		}
+	}
+
+	// Fill in the configured type names, which we need to do the rest of the work.
+	for _, ti := range toWrite {
+		if tc := conf.Types[ti.protoName]; tc != nil && tc.Name != "" {
+			ti.veneerName = tc.Name
+		}
+	}
+
+	// Sort for determinism.
+	sort.Slice(toWrite, func(i, j int) bool {
+		return toWrite[i].veneerName < toWrite[j].veneerName
+	})
+
+	// Process and configure all the types we care about.
+	// Even if there is no config for a type, there is still work to do.
+	for _, ti := range toWrite {
+		if err := processType(ti, conf.Types[ti.protoName], typeInfos); err != nil {
+			return nil, err
+		}
+	}
+
+	converters, err := buildConverterMap(toWrite, conf)
+	if err != nil {
+		return nil, err
+	}
+
+	// Use the converters map to give every field a converter.
+	for _, ti := range toWrite {
+		for _, f := range ti.fields {
+			f.converter, err = makeConverter(f.af.Type, f.protoType, converters)
+			if err != nil {
+				return nil, fmt.Errorf("%s.%s: %w", ti.protoName, f.protoName, err)
+			}
+		}
+	}
+
+	// Write the generated code.
+	return write(toWrite, conf, fset)
+}
+
+// buildConverterMap builds a map from veneer name to a converter, which writes code that converts between the proto and veneer.
+// This is used for fields when generating conversion functions.
+func buildConverterMap(typeInfos []*typeInfo, conf *config) (map[string]converter, error) {
+	converters := map[string]converter{}
+	// Build a converter for each proto type.
+	for _, ti := range typeInfos {
+		var conv converter
+		// Custom converters on the type take precedence.
+		if tc := conf.Types[ti.protoName]; tc != nil && tc.ConvertToFrom != "" {
+			c, err := parseCustomConverter(ti.veneerName, tc.ConvertToFrom)
+			if err != nil {
+				return nil, err
+			}
+			conv = c
+		} else {
+			switch ti.spec.Type.(type) {
+			case *ast.StructType:
+				conv = protoConverter{veneerName: ti.veneerName}
+			case *ast.Ident:
+				conv = enumConverter{protoName: ti.protoName, veneerName: ti.veneerName}
+			default:
+				conv = identityConverter{}
+			}
+		}
+		converters[ti.veneerName] = conv
+	}
+
+	// Add converters for used external types to the map.
+	for _, et := range externalTypes {
+		if et.used {
+			converters[et.qualifiedName] = customConverter{et.convertTo, et.convertFrom}
+		}
+	}
+
+	// Add custom converters to the map.
+	// These differ from custom converters on the proto types (a few lines above here)
+	// because they are keyed by veneer type, not proto type.
+	// That can matter when the proto type is omitted but there is a corresponding
+	// veneer type.
+	for key, value := range conf.Converters {
+		c, err := parseCustomConverter(key, value)
+		if err != nil {
+			return nil, err
+		}
+		converters[key] = c
+	}
+	return converters, nil
+}
+
+func parseCustomConverter(name, value string) (converter, error) {
+	toFunc, fromFunc, ok := strings.Cut(value, ",")
+	toFunc = strings.TrimSpace(toFunc)
+	fromFunc = strings.TrimSpace(fromFunc)
+	if !ok || toFunc == "" || fromFunc == "" {
+		return nil, fmt.Errorf(`%s: ConvertToFrom = %q, want "toFunc, fromFunc"`, name, value)
+	}
+	return customConverter{toFunc, fromFunc}, nil
+}
+
+// makeConverter constructs a converter for the given type. Not every type is in the map: this
+// function puts together converters for types like pointers, slices and maps, as well as
+// named types.
+func makeConverter(veneerType, protoType ast.Expr, converters map[string]converter) (converter, error) {
+	if c, ok := converters[typeString(veneerType)]; ok {
+		return c, nil
+	}
+	// If there is no converter for this type, look for a converter for a part of the type.
+	switch t := veneerType.(type) {
+	case *ast.Ident:
+		// Handle the case where the veneer type is the dereference of the proto type.
+		if se, ok := protoType.(*ast.StarExpr); ok {
+			if identName(se.X) != t.Name {
+				return nil, fmt.Errorf("veneer type %s does not match dereferenced proto type %s", t.Name, identName(se.X))
+			}
+			return derefConverter{}, nil
+		}
+		return identityConverter{}, nil
+	case *ast.StarExpr:
+		return makeConverter(t.X, protoType.(*ast.StarExpr).X, converters)
+	case *ast.ArrayType:
+		eltc, err := makeConverter(t.Elt, protoType.(*ast.ArrayType).Elt, converters)
+		if err != nil {
+			return nil, err
+		}
+		return sliceConverter{eltc}, nil
+	case *ast.MapType:
+		// Assume the key types are the same.
+		vc, err := makeConverter(t.Value, protoType.(*ast.MapType).Value, converters)
+		if err != nil {
+			return nil, err
+		}
+		return mapConverter{vc}, nil
+	default:
+		return identityConverter{}, nil
+	}
+}
+
+// A typeInfo holds information about a named type.
+type typeInfo struct {
+	// These fields are collected from the proto package.
+	protoName string        // name of type in the proto package
+	spec      *ast.TypeSpec // the spec for the type, which will be modified
+	decl      *ast.GenDecl  // the decl holding the spec; not sure we need this
+	values    *ast.GenDecl  // the list of values for an enum
+
+	// These fields are added later.
+	veneerName string       // may be provided by config; else same as protoName
+	fields     []*fieldInfo // for structs
+	valueNames []string     // to generate String functions
+}
+
+// A fieldInfo holds information about a struct field.
+type fieldInfo struct {
+	protoType             ast.Expr
+	af                    *ast.Field
+	protoName, veneerName string
+	converter             converter
+}
+
+// collectDecls collects declaration information from a package.
+// It returns information about every named type in the package in a map
+// keyed by the type's name.
+func collectDecls(pkg *ast.Package) (map[string]*typeInfo, error) {
+	typeInfos := map[string]*typeInfo{} // key is proto name
+
+	getInfo := func(name string) *typeInfo {
+		if info, ok := typeInfos[name]; ok {
+			return info
+		}
+		info := &typeInfo{protoName: name, veneerName: name}
+		typeInfos[name] = info
+		return info
+	}
+
+	for _, file := range pkg.Files {
+		for _, decl := range file.Decls {
+			if gd, ok := decl.(*ast.GenDecl); ok {
+				switch gd.Tok {
+				case token.TYPE:
+					if len(gd.Specs) != 1 {
+						return nil, errors.New("multiple TypeSpecs in a GenDecl not supported")
+					}
+					ts := gd.Specs[0].(*ast.TypeSpec)
+					info := getInfo(ts.Name.Name)
+					info.spec = ts
+					info.decl = gd
+
+				case token.CONST:
+					// Assume consts for an enum type are grouped together, and every one has a type.
+					// That's what the proto compiler generates.
+					vs0 := gd.Specs[0].(*ast.ValueSpec)
+					if len(vs0.Names) != 1 || len(vs0.Values) != 1 {
+						return nil, errors.New("multiple names/values not supported")
+					}
+
+					protoName := identName(vs0.Type)
+					if protoName == "" {
+						continue
+					}
+					for _, s := range gd.Specs {
+						vs := s.(*ast.ValueSpec)
+						if identName(vs.Type) != protoName {
+							return nil, fmt.Errorf("%s: not all same type", protoName)
+						}
+					}
+					info := getInfo(protoName)
+					info.values = gd
+				}
+			}
+		}
+	}
+	return typeInfos, nil
+}
+
+// processType processes a single type, modifying the AST.
+// If it's an enum, just change its name.
+// If it's a struct, modify its name and fields.
+func processType(ti *typeInfo, tconf *typeConfig, typeInfos map[string]*typeInfo) error {
+	ti.spec.Name.Name = ti.veneerName
+	switch t := ti.spec.Type.(type) {
+	case *ast.StructType:
+		// Check that all configured fields are present.
+		exportedFields := map[string]bool{}
+		for _, f := range t.Fields.List {
+			if len(f.Names) > 1 {
+				return fmt.Errorf("%s: multiple names in one field spec not supported: %v", ti.protoName, f.Names)
+			}
+			if f.Names[0].IsExported() {
+				exportedFields[f.Names[0].Name] = true
+			}
+		}
+		if tconf != nil {
+			for name := range tconf.Fields {
+				if !exportedFields[name] {
+					return fmt.Errorf("%s: configured field %s is not present", ti.protoName, name)
+				}
+			}
+		}
+		// Process the fields.
+		fs := t.Fields.List
+		t.Fields.List = t.Fields.List[:0]
+		for _, f := range fs {
+			fi, err := processField(f, tconf, typeInfos)
+			if err != nil {
+				return err
+			}
+			if fi != nil {
+				t.Fields.List = append(t.Fields.List, f)
+				ti.fields = append(ti.fields, fi)
+			}
+		}
+	case *ast.Ident:
+		// Enum type. Nothing else to do with the type itself; but see processEnumValues.
+	default:
+		return fmt.Errorf("unknown type: %+v: protoName=%s", ti.spec, ti.protoName)
+	}
+	processDoc(ti.decl, ti.protoName, tconf)
+	if ti.values != nil {
+		ti.valueNames = processEnumValues(ti.values, tconf)
+	}
+	return nil
+}
+
+// processField processes a struct field.
+func processField(af *ast.Field, tc *typeConfig, typeInfos map[string]*typeInfo) (*fieldInfo, error) {
+	id := af.Names[0]
+	if !id.IsExported() {
+		return nil, nil
+	}
+	fi := &fieldInfo{
+		protoType:  af.Type,
+		af:         af,
+		protoName:  id.Name,
+		veneerName: id.Name,
+	}
+	if tc != nil {
+		if fc, ok := tc.Fields[id.Name]; ok {
+			if fc.Omit {
+				return nil, nil
+			}
+			if fc.Name != "" {
+				id.Name = fc.Name
+				fi.veneerName = fc.Name
+			}
+			if fc.Type != "" {
+				expr, err := parser.ParseExpr(fc.Type)
+				if err != nil {
+					return nil, err
+				}
+				af.Type = expr
+			}
+		}
+	}
+	af.Type = veneerType(af.Type, typeInfos)
+	af.Tag = nil
+	return fi, nil
+}
+
+// veneerType returns a type expression for the veneer type corresponding to the given proto type.
+func veneerType(protoType ast.Expr, typeInfos map[string]*typeInfo) ast.Expr {
+	var wtype func(ast.Expr) ast.Expr
+	wtype = func(protoType ast.Expr) ast.Expr {
+		if et := protoTypeToExternalType[typeString(protoType)]; et != nil {
+			et.used = true
+			return et.typeExpr
+		}
+		switch t := protoType.(type) {
+		case *ast.Ident:
+			if ti := typeInfos[t.Name]; ti != nil {
+				wt := *t
+				wt.Name = ti.veneerName
+				return &wt
+			}
+		case *ast.ParenExpr:
+			wt := *t
+			wt.X = wtype(wt.X)
+			return &wt
+
+		case *ast.StarExpr:
+			wt := *t
+			wt.X = wtype(wt.X)
+			return &wt
+
+		case *ast.ArrayType:
+			wt := *t
+			wt.Elt = wtype(wt.Elt)
+			return &wt
+		}
+		return protoType
+	}
+
+	return wtype(protoType)
+}
+
+// processEnumValues processes enum values.
+// The proto compiler puts all the values for an enum in one GenDecl,
+// and there are no other values in that GenDecl.
+func processEnumValues(d *ast.GenDecl, tc *typeConfig) []string {
+	var valueNames []string
+	for _, s := range d.Specs {
+		vs := s.(*ast.ValueSpec)
+		id := vs.Names[0]
+		protoName := id.Name
+		veneerName := veneerValueName(id.Name, tc)
+		valueNames = append(valueNames, veneerName)
+		id.Name = veneerName
+
+		if tc != nil {
+			vs.Type.(*ast.Ident).Name = tc.Name
+		}
+		modifyCommentGroup(vs.Doc, protoName, veneerName, "means", "")
+	}
+	return valueNames
+}
+
+// veneerValueName returns an idiomatic Go name for a proto enum value.
+func veneerValueName(protoValueName string, tc *typeConfig) string {
+	if tc == nil {
+		return protoValueName
+	}
+	if nn, ok := tc.ValueNames[protoValueName]; ok {
+		return nn
+	}
+	name := strings.TrimPrefix(protoValueName, tc.ProtoPrefix)
+	// Some values have the type name in upper snake case after the prefix.
+	// Example:
+	//    proto type: FinishReason
+	//    prefix: Candidate_
+	//    value:  Candidate_FINISH_REASON_UNSPECIFIED
+	prefix := camelToUpperSnakeCase(tc.Name) + "_"
+	name = strings.TrimPrefix(name, prefix)
+	return tc.VeneerPrefix + snakeToCamelCase(name)
+}
+
+func processDoc(gd *ast.GenDecl, protoName string, tc *typeConfig) {
+	doc := ""
+	verb := ""
+	if tc != nil {
+		doc = tc.Doc
+		verb = tc.DocVerb
+	}
+
+	spec := gd.Specs[0]
+	var name string
+	switch spec := spec.(type) {
+	case *ast.TypeSpec:
+		name = spec.Name.Name
+	case *ast.ValueSpec:
+		name = spec.Names[0].Name
+	default:
+		panic("bad spec")
+	}
+	if tc != nil && name != tc.Name {
+		panic(fmt.Errorf("GenDecl name is %q, config name is %q", name, tc.Name))
+	}
+	modifyCommentGroup(gd.Doc, protoName, name, verb, doc)
+}
+
+func modifyCommentGroup(cg *ast.CommentGroup, protoName, veneerName, verb, doc string) {
+	if cg == nil {
+		return
+	}
+	if len(cg.List) == 0 {
+		return
+	}
+	c := cg.List[0]
+	c.Text = "// " + adjustDoc(strings.TrimPrefix(c.Text, "// "), protoName, veneerName, verb, doc)
+}
+
+// adjustDoc takes a doc string with initial comment characters and whitespace removed, and returns
+// a replacement that uses the given veneer name, verb and new doc string.
+func adjustDoc(origDoc, protoName, veneerName, verb, newDoc string) string {
+	// if newDoc is non-empty, completely replace the existing doc.
+	if newDoc != "" {
+		return veneerName + " " + newDoc
+	}
+	// If the doc string starts with the proto name, just replace it with the
+	// veneer name. We can't do anything about the verb because we don't know
+	// where it is in the original doc string. (I guess we could assume it's the
+	// next word, but that might not always work.)
+	if strings.HasPrefix(origDoc, protoName+" ") {
+		return veneerName + origDoc[len(protoName):]
+	}
+
+	// Lowercase the first letter of the given doc if it's not part of an acronym.
+	runes := []rune(origDoc)
+	// It shouldn't be possible for the original doc string to be empty,
+	// but check just in case to avoid panics.
+	if len(runes) == 0 {
+		return origDoc
+	}
+	// Heuristic: an acronym begins with two consecutive uppercase letters.
+	if unicode.IsUpper(runes[0]) && (len(runes) == 1 || !unicode.IsUpper(runes[1])) {
+		runes[0] = unicode.ToLower(runes[0])
+		origDoc = string(runes)
+	}
+
+	if verb == "" {
+		verb = "is"
+	}
+	return fmt.Sprintf("%s %s %s", veneerName, verb, origDoc)
+}
+
+////////////////////////////////////////////////////////////////
+
+const licenseFormat = `// Copyright %d Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+`
+
+func write(typeInfos []*typeInfo, conf *config, fset *token.FileSet) ([]byte, error) {
+	var buf bytes.Buffer
+	pr := func(format string, args ...any) { fmt.Fprintf(&buf, format, args...) }
+	prn := func(format string, args ...any) {
+		pr(format, args...)
+		pr("\n")
+	}
+	// Top of file.
+	pr(licenseFormat, time.Now().Year())
+	prn("")
+	pr("// This file was generated by protoveneer. DO NOT EDIT.\n\n")
+	pr("package %s\n\n", conf.Package)
+	prn("import (")
+	prn(`    "fmt"`)
+	pr("\n")
+	prn(`    pb "%s"`, conf.ProtoImportPath)
+	if conf.SupportImportPath == "" {
+		return nil, errors.New("missing supportImportPath in config")
+	}
+	prn(`    "%s"`, conf.SupportImportPath)
+	for _, et := range externalTypes {
+		if et.used && et.importPath != "" {
+			prn(`    "%s"`, et.importPath)
+		}
+	}
+	pr(")\n\n")
+
+	// Types.
+	for _, ti := range typeInfos {
+		for _, decl := range []*ast.GenDecl{ti.decl, ti.values} {
+			if decl != nil {
+				data, err := formatDecl(fset, decl)
+				if err != nil {
+					return nil, err
+				}
+				buf.Write(data)
+				prn("")
+			}
+		}
+		if ti.valueNames != nil {
+			if err := generateEnumStringMethod(&buf, ti.veneerName, ti.valueNames); err != nil {
+				return nil, err
+			}
+		}
+		if _, ok := ti.spec.Type.(*ast.StructType); ok {
+			ti.generateConversionMethods(pr)
+		}
+	}
+
+	return buf.Bytes(), nil
+}
+
+func formatDecl(fset *token.FileSet, gd *ast.GenDecl) ([]byte, error) {
+	var buf bytes.Buffer
+	if err := format.Node(&buf, fset, gd); err != nil {
+		return nil, err
+	}
+	// Remove blank lines that result from deleting unexported struct fields.
+	return bytes.ReplaceAll(buf.Bytes(), []byte("\n\n"), []byte("\n")), nil
+}
+
+////////////////////////////////////////////////////////////////
+
+var stringMethodTemplate = template.Must(template.New("").Parse(`
+	var namesFor{{.Type}} = map[{{.Type}}]string {
+		{{- range .Values}}
+			{{.}}: "{{.}}",
+		{{- end}}
+	}
+
+	func (v {{.Type}}) String() string {
+		if n, ok := namesFor{{.Type}}[v]; ok {
+			return n
+		}
+		return fmt.Sprintf("{{.Type}}(%d)", v)
+	}
+`))
+
+func generateEnumStringMethod(w io.Writer, typeName string, valueNames []string) error {
+	return stringMethodTemplate.Execute(w, struct {
+		Type   string
+		Values []string
+	}{typeName, valueNames})
+}
+
+func (ti *typeInfo) generateConversionMethods(pr func(string, ...any)) {
+	ti.generateToProto(pr)
+	pr("\n")
+	ti.generateFromProto(pr)
+}
+
+func (ti *typeInfo) generateToProto(pr func(string, ...any)) {
+	pr("func (v *%s) toProto() *pb.%s {\n", ti.veneerName, ti.protoName)
+	pr("  if v == nil { return nil }\n")
+	pr("  return &pb.%s{\n", ti.protoName)
+	for _, f := range ti.fields {
+		pr("        %s: %s,\n", f.protoName, f.converter.genTo("v."+f.veneerName))
+	}
+	pr("    }\n")
+	pr("}\n")
+}
+
+func (ti *typeInfo) generateFromProto(pr func(string, ...any)) {
+	pr("func (%s) fromProto(p *pb.%s) *%[1]s {\n", ti.veneerName, ti.protoName)
+	pr("  if p == nil { return nil }\n")
+	pr("  return &%s{\n", ti.veneerName)
+	for _, f := range ti.fields {
+		pr("        %s: %s,\n", f.veneerName, f.converter.genFrom("p."+f.protoName))
+	}
+	pr("    }\n")
+	pr("}\n")
+}
+
+////////////////////////////////////////////////////////////////
+
+// externalType holds information about a type that is not part of the proto package.
+type externalType struct {
+	qualifiedName string
+	replaces      string
+	importPath    string
+	convertTo     string
+	convertFrom   string
+
+	typeExpr ast.Expr
+	used     bool
+}
+
+var externalTypes = []*externalType{
+	{
+		qualifiedName: "civil.Date",
+		replaces:      "*date.Date",
+		importPath:    "cloud.google.com/go/civil",
+		convertTo:     "support.CivilDateToProto",
+		convertFrom:   "support.CivilDateFromProto",
+	},
+	{
+		qualifiedName: "map[string]any",
+		replaces:      "*structpb.Struct",
+		convertTo:     "support.MapToStructPB",
+		convertFrom:   "support.MapFromStructPB",
+	},
+}
+
+var protoTypeToExternalType = map[string]*externalType{}
+
+func init() {
+	var err error
+	for _, et := range externalTypes {
+		et.typeExpr, err = parser.ParseExpr(et.qualifiedName)
+		if err != nil {
+			panic(err)
+		}
+		protoTypeToExternalType[et.replaces] = et
+	}
+}
+
+////////////////////////////////////////////////////////////////
+
+var emptyFileSet = token.NewFileSet()
+
+// typeString produces a string for a type expression.
+func typeString(t ast.Expr) string {
+	var buf bytes.Buffer
+	err := format.Node(&buf, emptyFileSet, t)
+	if err != nil {
+		panic(err)
+	}
+	return buf.String()
+}
+
+func identName(x any) string {
+	id, ok := x.(*ast.Ident)
+	if !ok {
+		return ""
+	}
+	return id.Name
+}
+
+func snakeToCamelCase(s string) string {
+	words := strings.Split(s, "_")
+	for i, w := range words {
+		if len(w) == 0 {
+			words[i] = w
+		} else {
+			words[i] = fmt.Sprintf("%c%s", unicode.ToUpper(rune(w[0])), strings.ToLower(w[1:]))
+		}
+	}
+	return strings.Join(words, "")
+}
+
+func camelToUpperSnakeCase(s string) string {
+	var res []rune
+	for i, r := range s {
+		if unicode.IsUpper(r) && i > 0 {
+			res = append(res, '_')
+		}
+		res = append(res, unicode.ToUpper(r))
+	}
+	return string(res)
+}
+
+func sliceAnyError[T any](s []T, f func(T) (bool, error)) (bool, error) {
+	for _, e := range s {
+		b, err := f(e)
+		if err != nil {
+			return false, err
+		}
+		if b {
+			return true, nil
+		}
+	}
+	return false, nil
+}
diff --git a/protoveneer/cmd/protoveneer/protoveneer_test.go b/protoveneer/cmd/protoveneer/protoveneer_test.go
new file mode 100644
index 0000000..75c7d9b
--- /dev/null
+++ b/protoveneer/cmd/protoveneer/protoveneer_test.go
@@ -0,0 +1,136 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"context"
+	"flag"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+var (
+	update = flag.Bool("update", false, "update test goldens")
+	keep   = flag.Bool("keep", false, "do not remove generated files")
+)
+
+func TestGeneration(t *testing.T) {
+	ctx := context.Background()
+	entries, err := os.ReadDir("testdata")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, e := range entries {
+		if e.IsDir() {
+			t.Run(e.Name(), func(t *testing.T) {
+				dir := filepath.Join("testdata", e.Name())
+				configFile := filepath.Join(dir, "config.yaml")
+				goldenFile := filepath.Join(dir, "golden")
+				outFile := filepath.Join(dir, e.Name()+"_veneer.gen.go")
+				if *keep {
+					t.Logf("keeping %s", outFile)
+				} else {
+					defer os.Remove(outFile)
+				}
+				if err := run(ctx, configFile, dir, dir); err != nil {
+					t.Fatal(err)
+				}
+				if *update {
+					if err := os.Remove(goldenFile); err != nil {
+						t.Fatal(err)
+					}
+					if err := os.Rename(outFile, goldenFile); err != nil {
+						t.Fatal(err)
+					}
+					t.Logf("updated golden")
+				} else {
+					if diff := diffFiles(goldenFile, outFile); diff != "" {
+						t.Errorf("diff (-want, +got):\n%s", diff)
+					}
+				}
+			})
+		}
+	}
+}
+
+func diffFiles(wantFile, gotFile string) string {
+	want, err := os.ReadFile(wantFile)
+	if err != nil {
+		return err.Error()
+	}
+	got, err := os.ReadFile(gotFile)
+	if err != nil {
+		return err.Error()
+	}
+	return cmp.Diff(string(want), string(got))
+}
+
+func TestCamelToUpperSnakeCase(t *testing.T) {
+	for _, test := range []struct {
+		in, want string
+	}{
+		{"foo", "FOO"},
+		{"fooBar", "FOO_BAR"},
+		{"aBC", "A_B_C"},
+		{"ABC", "A_B_C"},
+	} {
+		got := camelToUpperSnakeCase(test.in)
+		if got != test.want {
+			t.Errorf("%q: got %q, want %q", test.in, got, test.want)
+		}
+	}
+}
+
+func TestAdjustDoc(t *testing.T) {
+	const protoName = "PName"
+	const veneerName = "VName"
+	for i, test := range []struct {
+		origDoc string
+		verb    string
+		newDoc  string
+		want    string
+	}{
+		{
+			origDoc: "",
+			verb:    "foo",
+			newDoc:  "",
+			want:    "",
+		},
+		{
+			origDoc: "",
+			verb:    "",
+			newDoc:  "is new doc.",
+			want:    "VName is new doc.",
+		},
+		{
+			origDoc: "The harm category is dangerous content.",
+			verb:    "means",
+			want:    "VName means the harm category is dangerous content.",
+		},
+		{
+			origDoc: "URI for the file.",
+			verb:    "is the",
+			want:    "VName is the URI for the file.",
+		},
+		{
+			origDoc: "PName is a thing.",
+			newDoc:  "contains something else.",
+			want:    "VName contains something else.",
+		},
+		{
+			origDoc: "PName is a thing.",
+			verb:    "ignored",
+			want:    "VName is a thing.",
+		},
+	} {
+		got := adjustDoc(test.origDoc, protoName, veneerName, test.verb, test.newDoc)
+		if got != test.want {
+			t.Errorf("#%d: got %q, want %q", i, got, test.want)
+		}
+	}
+}
diff --git a/protoveneer/cmd/protoveneer/testdata/basic/basic.pb.go b/protoveneer/cmd/protoveneer/testdata/basic/basic.pb.go
new file mode 100755
index 0000000..25f0c75
--- /dev/null
+++ b/protoveneer/cmd/protoveneer/testdata/basic/basic.pb.go
@@ -0,0 +1,122 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package basic
+
+import (
+	_ "google.golang.org/genproto/googleapis/api/annotations"
+	date "google.golang.org/genproto/googleapis/type/date"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	"google.golang.org/protobuf/types/known/structpb"
+)
+
+const (
+	// Verify that this generated code is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
+	// Verify that runtime/protoimpl is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
+)
+
+// Harm categories that will block the content.
+type HarmCategory int32
+
+const (
+	// The harm category is unspecified.
+	HarmCategory_HARM_CATEGORY_UNSPECIFIED HarmCategory = 0
+	// The harm category is hate speech.
+	HarmCategory_HARM_CATEGORY_HATE_SPEECH HarmCategory = 1
+	// The harm category is dangerous content.
+	HarmCategory_HARM_CATEGORY_DANGEROUS_CONTENT HarmCategory = 2
+	// The harm category is harassment.
+	HarmCategory_HARM_CATEGORY_HARASSMENT HarmCategory = 3
+	// The harm category is sexually explicit content.
+	HarmCategory_HARM_CATEGORY_SEXUALLY_EXPLICIT HarmCategory = 4
+)
+
+// The reason why the model stopped generating tokens.
+// If empty, the model has not stopped generating the tokens.
+type Candidate_FinishReason int32
+
+const (
+	// The finish reason is unspecified.
+	Candidate_FINISH_REASON_UNSPECIFIED Candidate_FinishReason = 0
+	// Natural stop point of the model or provided stop sequence.
+	Candidate_STOP Candidate_FinishReason = 1
+	// The maximum number of tokens as specified in the request was reached.
+	Candidate_MAX_TOKENS Candidate_FinishReason = 2
+	// The token generation was stopped as the response was flagged for safety
+	// reasons. NOTE: When streaming the Candidate.content will be empty if
+	// content filters blocked the output.
+	Candidate_SAFETY Candidate_FinishReason = 3
+	// The token generation was stopped as the response was flagged for
+	// unauthorized citations.
+	Candidate_RECITATION Candidate_FinishReason = 4
+	// All other reasons that stopped the token generation
+	Candidate_OTHER Candidate_FinishReason = 5
+)
+
+// Raw media bytes.
+//
+// Text should not be sent as raw bytes, use the 'text' field.
+type Blob struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// Required. The IANA standard MIME type of the source data.
+	MimeType string `protobuf:"bytes,1,opt,name=mime_type,json=mimeType,proto3" json:"mime_type,omitempty"`
+	// Required. Raw bytes for media formats.
+	Data []byte `protobuf:"bytes,2,opt,name=data,proto3" json:"data,omitempty"`
+}
+
+// Generation config.
+type GenerationConfig struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// Optional. Controls the randomness of predictions.
+	Temperature *float32 `protobuf:"fixed32,1,opt,name=temperature,proto3,oneof" json:"temperature,omitempty"`
+	// Optional. Number of candidates to generate.
+	CandidateCount *int32 `protobuf:"varint,4,opt,name=candidate_count,json=candidateCount,proto3,oneof" json:"candidate_count,omitempty"`
+	// Optional. Stop sequences.
+	StopSequences []string `protobuf:"bytes,6,rep,name=stop_sequences,json=stopSequences,proto3" json:"stop_sequences,omitempty"`
+	HarmCat       HarmCategory
+	FinishReason  Candidate_FinishReason
+	CitMet        *CitationMetadata
+}
+
+// A collection of source attributions for a piece of content.
+type CitationMetadata struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// Output only. List of citations.
+	Citations []*Citation `protobuf:"bytes,1,rep,name=citations,proto3" json:"citations,omitempty"`
+	CitMap    map[string]*Citation
+}
+
+// Source attributions for content.
+type Citation struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// Output only. Url reference of the attribution.
+	Uri string `protobuf:"bytes,3,opt,name=uri,proto3" json:"uri,omitempty"`
+	// Output only. Publication date of the attribution.
+	PublicationDate *date.Date `protobuf:"bytes,6,opt,name=publication_date,json=publicationDate,proto3" json:"publication_date,omitempty"`
+	Struct          *structpb.Struct
+}
diff --git a/protoveneer/cmd/protoveneer/testdata/basic/config.yaml b/protoveneer/cmd/protoveneer/testdata/basic/config.yaml
new file mode 100644
index 0000000..9a54cbe
--- /dev/null
+++ b/protoveneer/cmd/protoveneer/testdata/basic/config.yaml
@@ -0,0 +1,45 @@
+# Copyright 2023 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+package: basic
+protoImportPath: example.com/basic
+supportImportPath: example.com/protoveneer/support
+
+types:
+    HarmCategory:
+      protoPrefix: HarmCategory_HARM_CATEGORY_
+      docVerb: specifies
+
+    Candidate_FinishReason:
+      name: FinishReason
+      protoPrefix: Candidate_
+
+    Blob:
+      fields:
+        MimeType:
+          name: MIMEType
+      docVerb: contains
+
+    GenerationConfig:
+      fields:
+        Temperature:
+          type: float32
+        CandidateCount:
+          type: int32
+
+    Citation:
+      docVerb: contains
+      fields:
+        Uri:
+          name: URI
diff --git a/protoveneer/cmd/protoveneer/testdata/basic/golden b/protoveneer/cmd/protoveneer/testdata/basic/golden
new file mode 100644
index 0000000..ec4b158
--- /dev/null
+++ b/protoveneer/cmd/protoveneer/testdata/basic/golden
@@ -0,0 +1,223 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This file was generated by protoveneer. DO NOT EDIT.
+
+package basic
+
+import (
+	"fmt"
+
+	"cloud.google.com/go/civil"
+	pb "example.com/basic"
+	"example.com/protoveneer/support"
+)
+
+// Blob contains raw media bytes.
+//
+// Text should not be sent as raw bytes, use the 'text' field.
+type Blob struct {
+	// Required. The IANA standard MIME type of the source data.
+	MIMEType string
+	// Required. Raw bytes for media formats.
+	Data []byte
+}
+
+func (v *Blob) toProto() *pb.Blob {
+	if v == nil {
+		return nil
+	}
+	return &pb.Blob{
+		MimeType: v.MIMEType,
+		Data:     v.Data,
+	}
+}
+
+func (Blob) fromProto(p *pb.Blob) *Blob {
+	if p == nil {
+		return nil
+	}
+	return &Blob{
+		MIMEType: p.MimeType,
+		Data:     p.Data,
+	}
+}
+
+// Citation contains source attributions for content.
+type Citation struct {
+	// Output only. Url reference of the attribution.
+	URI string
+	// Output only. Publication date of the attribution.
+	PublicationDate civil.Date
+	Struct          map[string]any
+}
+
+func (v *Citation) toProto() *pb.Citation {
+	if v == nil {
+		return nil
+	}
+	return &pb.Citation{
+		Uri:             v.URI,
+		PublicationDate: support.CivilDateToProto(v.PublicationDate),
+		Struct:          support.MapToStructPB(v.Struct),
+	}
+}
+
+func (Citation) fromProto(p *pb.Citation) *Citation {
+	if p == nil {
+		return nil
+	}
+	return &Citation{
+		URI:             p.Uri,
+		PublicationDate: support.CivilDateFromProto(p.PublicationDate),
+		Struct:          support.MapFromStructPB(p.Struct),
+	}
+}
+
+// CitationMetadata is a collection of source attributions for a piece of content.
+type CitationMetadata struct {
+	// Output only. List of citations.
+	Citations []*Citation
+	CitMap    map[string]*Citation
+}
+
+func (v *CitationMetadata) toProto() *pb.CitationMetadata {
+	if v == nil {
+		return nil
+	}
+	return &pb.CitationMetadata{
+		Citations: support.TransformSlice(v.Citations, (*Citation).toProto),
+		CitMap:    support.TransformMapValues(v.CitMap, (*Citation).toProto),
+	}
+}
+
+func (CitationMetadata) fromProto(p *pb.CitationMetadata) *CitationMetadata {
+	if p == nil {
+		return nil
+	}
+	return &CitationMetadata{
+		Citations: support.TransformSlice(p.Citations, (Citation{}).fromProto),
+		CitMap:    support.TransformMapValues(p.CitMap, (Citation{}).fromProto),
+	}
+}
+
+// FinishReason is the reason why the model stopped generating tokens.
+// If empty, the model has not stopped generating the tokens.
+type FinishReason int32
+
+const (
+	// FinishReasonUnspecified means the finish reason is unspecified.
+	FinishReasonUnspecified FinishReason = 0
+	// FinishReasonStop means natural stop point of the model or provided stop sequence.
+	FinishReasonStop FinishReason = 1
+	// FinishReasonMaxTokens means the maximum number of tokens as specified in the request was reached.
+	FinishReasonMaxTokens FinishReason = 2
+	// FinishReasonSafety means the token generation was stopped as the response was flagged for safety
+	// reasons. NOTE: When streaming the Candidate.content will be empty if
+	// content filters blocked the output.
+	FinishReasonSafety FinishReason = 3
+	// FinishReasonRecitation means the token generation was stopped as the response was flagged for
+	// unauthorized citations.
+	FinishReasonRecitation FinishReason = 4
+	// FinishReasonOther means all other reasons that stopped the token generation
+	FinishReasonOther FinishReason = 5
+)
+
+var namesForFinishReason = map[FinishReason]string{
+	FinishReasonUnspecified: "FinishReasonUnspecified",
+	FinishReasonStop:        "FinishReasonStop",
+	FinishReasonMaxTokens:   "FinishReasonMaxTokens",
+	FinishReasonSafety:      "FinishReasonSafety",
+	FinishReasonRecitation:  "FinishReasonRecitation",
+	FinishReasonOther:       "FinishReasonOther",
+}
+
+func (v FinishReason) String() string {
+	if n, ok := namesForFinishReason[v]; ok {
+		return n
+	}
+	return fmt.Sprintf("FinishReason(%d)", v)
+}
+
+// GenerationConfig is generation config.
+type GenerationConfig struct {
+	// Optional. Controls the randomness of predictions.
+	Temperature float32
+	// Optional. Number of candidates to generate.
+	CandidateCount int32
+	// Optional. Stop sequences.
+	StopSequences []string
+	HarmCat       HarmCategory
+	FinishReason  FinishReason
+	CitMet        *CitationMetadata
+}
+
+func (v *GenerationConfig) toProto() *pb.GenerationConfig {
+	if v == nil {
+		return nil
+	}
+	return &pb.GenerationConfig{
+		Temperature:    support.AddrOrNil(v.Temperature),
+		CandidateCount: support.AddrOrNil(v.CandidateCount),
+		StopSequences:  v.StopSequences,
+		HarmCat:        pb.HarmCategory(v.HarmCat),
+		FinishReason:   pb.Candidate_FinishReason(v.FinishReason),
+		CitMet:         v.CitMet.toProto(),
+	}
+}
+
+func (GenerationConfig) fromProto(p *pb.GenerationConfig) *GenerationConfig {
+	if p == nil {
+		return nil
+	}
+	return &GenerationConfig{
+		Temperature:    support.DerefOrZero(p.Temperature),
+		CandidateCount: support.DerefOrZero(p.CandidateCount),
+		StopSequences:  p.StopSequences,
+		HarmCat:        HarmCategory(p.HarmCat),
+		FinishReason:   FinishReason(p.FinishReason),
+		CitMet:         (CitationMetadata{}).fromProto(p.CitMet),
+	}
+}
+
+// HarmCategory specifies harm categories that will block the content.
+type HarmCategory int32
+
+const (
+	// HarmCategoryUnspecified means the harm category is unspecified.
+	HarmCategoryUnspecified HarmCategory = 0
+	// HarmCategoryHateSpeech means the harm category is hate speech.
+	HarmCategoryHateSpeech HarmCategory = 1
+	// HarmCategoryDangerousContent means the harm category is dangerous content.
+	HarmCategoryDangerousContent HarmCategory = 2
+	// HarmCategoryHarassment means the harm category is harassment.
+	HarmCategoryHarassment HarmCategory = 3
+	// HarmCategorySexuallyExplicit means the harm category is sexually explicit content.
+	HarmCategorySexuallyExplicit HarmCategory = 4
+)
+
+var namesForHarmCategory = map[HarmCategory]string{
+	HarmCategoryUnspecified:      "HarmCategoryUnspecified",
+	HarmCategoryHateSpeech:       "HarmCategoryHateSpeech",
+	HarmCategoryDangerousContent: "HarmCategoryDangerousContent",
+	HarmCategoryHarassment:       "HarmCategoryHarassment",
+	HarmCategorySexuallyExplicit: "HarmCategorySexuallyExplicit",
+}
+
+func (v HarmCategory) String() string {
+	if n, ok := namesForHarmCategory[v]; ok {
+		return n
+	}
+	return fmt.Sprintf("HarmCategory(%d)", v)
+}
diff --git a/protoveneer/go.mod b/protoveneer/go.mod
new file mode 100644
index 0000000..03579fb
--- /dev/null
+++ b/protoveneer/go.mod
@@ -0,0 +1,11 @@
+module golang.org/x/exp/protoveneer
+
+go 1.21
+
+require (
+	cloud.google.com/go v0.111.0
+	github.com/google/go-cmp v0.6.0
+	google.golang.org/genproto v0.0.0-20231212172506-995d672761c0
+	google.golang.org/protobuf v1.31.0
+	gopkg.in/yaml.v3 v3.0.1
+)
diff --git a/protoveneer/go.sum b/protoveneer/go.sum
new file mode 100644
index 0000000..b6f598c
--- /dev/null
+++ b/protoveneer/go.sum
@@ -0,0 +1,16 @@
+cloud.google.com/go v0.111.0 h1:YHLKNupSD1KqjDbQ3+LVdQ81h/UJbJyZG203cEfnQgM=
+cloud.google.com/go v0.111.0/go.mod h1:0mibmpKP1TyOOFYQY5izo0LnT+ecvOQ0Sg3OdmMiNRU=
+github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
+github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+google.golang.org/genproto v0.0.0-20231212172506-995d672761c0 h1:YJ5pD9rF8o9Qtta0Cmy9rdBwkSjrTCT6XTiUQVOtIos=
+google.golang.org/genproto v0.0.0-20231212172506-995d672761c0/go.mod h1:l/k7rMz0vFTBPy+tFSGvXEd3z+BcoG1k7EHbqm+YBsY=
+google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp09yW+WbY/TyQbw=
+google.golang.org/protobuf v1.31.0 h1:g0LDEJHgrBl9N9r17Ru3sqWhkIx2NB67okBHPwC7hs8=
+google.golang.org/protobuf v1.31.0/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqwMG9pJV4I=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/protoveneer/support/support.go b/protoveneer/support/support.go
new file mode 100644
index 0000000..5e74f3b
--- /dev/null
+++ b/protoveneer/support/support.go
@@ -0,0 +1,112 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package support provides support functions for protoveneer.
+package support
+
+import (
+	"fmt"
+	"time"
+
+	"cloud.google.com/go/civil"
+	"google.golang.org/genproto/googleapis/type/date"
+	"google.golang.org/protobuf/types/known/structpb"
+)
+
+// TransformSlice applies f to each element of from and returns
+// a new slice with the results.
+func TransformSlice[From, To any](from []From, f func(From) To) []To {
+	if from == nil {
+		return nil
+	}
+	to := make([]To, len(from))
+	for i, e := range from {
+		to[i] = f(e)
+	}
+	return to
+}
+
+// TransformMapValues applies f to each value of from, returning a new map.
+// It does not change the keys.
+func TransformMapValues[K comparable, VFrom, VTo any](from map[K]VFrom, f func(VFrom) VTo) map[K]VTo {
+	if from == nil {
+		return nil
+	}
+	to := map[K]VTo{}
+	for k, v := range from {
+		to[k] = f(v)
+	}
+	return to
+}
+
+// AddrOrNil returns nil if x is the zero value for T,
+// or &x otherwise.
+func AddrOrNil[T comparable](x T) *T {
+	var z T
+	if x == z {
+		return nil
+	}
+	return &x
+}
+
+// DerefOrZero returns the zero value for T if x is nil,
+// or *x otherwise.
+func DerefOrZero[T any](x *T) T {
+	if x == nil {
+		var z T
+		return z
+	}
+	return *x
+}
+
+// CivilDateToProto converts a civil.Date to a date.Date.
+func CivilDateToProto(d civil.Date) *date.Date {
+	return &date.Date{
+		Year:  int32(d.Year),
+		Month: int32(d.Month),
+		Day:   int32(d.Day),
+	}
+}
+
+// CivilDateFromProto converts a date.Date to a civil.Date.
+func CivilDateFromProto(p *date.Date) civil.Date {
+	if p == nil {
+		return civil.Date{}
+	}
+	return civil.Date{
+		Year:  int(p.Year),
+		Month: time.Month(p.Month),
+		Day:   int(p.Day),
+	}
+}
+
+// MapToStructPB converts a map into a structpb.Struct.
+func MapToStructPB(m map[string]any) *structpb.Struct {
+	if m == nil {
+		return nil
+	}
+	s, err := structpb.NewStruct(m)
+	if err != nil {
+		panic(fmt.Errorf("support.MapToProto: %w", err))
+	}
+	return s
+}
+
+// MapFromStructPB converts a structpb.Struct to a map.
+func MapFromStructPB(p *structpb.Struct) map[string]any {
+	if p == nil {
+		return nil
+	}
+	return p.AsMap()
+}
diff --git a/protoveneer/support/support_test.go b/protoveneer/support/support_test.go
new file mode 100644
index 0000000..c3def96
--- /dev/null
+++ b/protoveneer/support/support_test.go
@@ -0,0 +1,35 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package support
+
+import (
+	"reflect"
+	"strconv"
+	"testing"
+)
+
+func TestTransformMapValues(t *testing.T) {
+	var from map[string]int
+	got := TransformMapValues(from, strconv.Itoa)
+	if got != nil {
+		t.Fatalf("got %v, want nil", got)
+	}
+	from = map[string]int{"one": 1, "two": 2}
+	got = TransformMapValues(from, strconv.Itoa)
+	want := map[string]string{"one": "1", "two": "2"}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, want %v", got, want)
+	}
+}