diff --git a/syntax/api_dump.go b/syntax/api_dump.go
new file mode 100644
index 000000000..ba63921ef
--- /dev/null
+++ b/syntax/api_dump.go
@@ -0,0 +1,214 @@
+// Copyright (c) 2019, Daniel Martí <mvdan@mvdan.cc>
+// See LICENSE for licensing information
+
+// +build ignore
+
+// api_dump is a simple program to create a description of what the syntax
+// package's API is. The main purpose is so that the JS package users can
+// inspect the API programmatically, to generate documentation, code, etc.
+//
+// To run with Go 1.11 or later: GO111MODULE=on go run api_dump.go
+
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"go/types"
+	"os"
+	"reflect"
+
+	"golang.org/x/tools/go/packages"
+)
+
+type Package struct {
+	Types map[string]NamedType `json:"types"`
+	Funcs map[string]DocType   `json:"funcs"`
+}
+
+type NamedType struct {
+	Doc  string      `json:"doc"`
+	Type interface{} `json:"type"`
+
+	EnumValues   []string `json:"enumvalues,omitempty"`
+	Implementers []string `json:"implementers,omitempty"`
+
+	Methods map[string]DocType `json:"methods"`
+}
+
+type DocType struct {
+	Doc  string      `json:"doc"`
+	Type interface{} `json:"type"`
+}
+
+func main() {
+	cfg := &packages.Config{Mode: packages.LoadSyntax}
+	pkgs, err := packages.Load(cfg, ".")
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	if packages.PrintErrors(pkgs) > 0 {
+		os.Exit(1)
+	}
+	if len(pkgs) != 1 {
+		panic("expected exactly one package")
+	}
+
+	dump := &Package{
+		Types: map[string]NamedType{},
+		Funcs: map[string]DocType{},
+	}
+
+	pkg := pkgs[0]
+	scope := pkg.Types.Scope()
+	var allImpls []*types.Pointer
+	var allConsts []*types.Const
+
+	for _, name := range scope.Names() {
+		obj := scope.Lookup(name)
+		if !obj.Exported() {
+			continue
+		}
+		switch obj := obj.(type) {
+		case *types.TypeName:
+			// not interfaces
+			if _, ok := obj.Type().(*types.Interface); !ok {
+				// include pointer receivers too
+				allImpls = append(allImpls, types.NewPointer(obj.Type()))
+			}
+		case *types.Const:
+			allConsts = append(allConsts, obj)
+		}
+	}
+
+	for _, name := range scope.Names() {
+		obj := scope.Lookup(name)
+		if !obj.Exported() {
+			continue
+		}
+		if fn, ok := obj.(*types.Func); ok {
+			dump.Funcs[fn.Name()] = DocType{
+				Type: dumpType(fn.Type()),
+			}
+			continue
+		}
+		tname, ok := obj.(*types.TypeName)
+		if !ok {
+			continue
+		}
+		name := tname.Name()
+		named, ok := obj.Type().(*types.Named)
+		if !ok {
+			continue
+		}
+
+		under := named.Underlying()
+		dumpNamed := NamedType{
+			Type:    dumpType(under),
+			Methods: map[string]DocType{},
+		}
+		switch under := under.(type) {
+		case *types.Basic:
+			if under.Info()&types.IsInteger == 0 {
+				break
+			}
+			for _, cnst := range allConsts {
+				if cnst.Type() == named {
+					dumpNamed.EnumValues = append(dumpNamed.EnumValues, cnst.Name())
+				}
+			}
+		case *types.Interface:
+			for _, typ := range allImpls {
+				if types.Implements(typ, under) {
+					dumpNamed.Implementers = append(dumpNamed.Implementers, typ.Elem().String())
+				}
+			}
+		}
+		for i := 0; i < named.NumMethods(); i++ {
+			fn := named.Method(i)
+			if !fn.Exported() {
+				continue
+			}
+			dumpNamed.Methods[fn.Name()] = DocType{
+				Type: dumpType(fn.Type()),
+			}
+		}
+		dump.Types[name] = dumpNamed
+	}
+	enc := json.NewEncoder(os.Stdout)
+	enc.SetIndent("", "\t")
+	if err := enc.Encode(dump); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+	}
+}
+
+func dumpType(typ types.Type) interface{} {
+	dump := map[string]interface{}{}
+	switch typ := typ.(type) {
+	case *types.Interface:
+		dump["kind"] = "interface"
+		methods := map[string]DocType{}
+		for i := 0; i < typ.NumMethods(); i++ {
+			fn := typ.Method(i)
+			if !fn.Exported() {
+				continue
+			}
+			methods[fn.Name()] = DocType{
+				Type: dumpType(fn.Type()),
+			}
+		}
+		dump["methods"] = methods
+		return dump
+	case *types.Struct:
+		dump["kind"] = "struct"
+		type Field struct {
+			Doc      string      `json:"doc"`
+			Type     interface{} `json:"type"`
+			Embedded bool        `json:"embedded"`
+		}
+		fields := map[string]Field{}
+		for i := 0; i < typ.NumFields(); i++ {
+			fd := typ.Field(i)
+			if !fd.Exported() {
+				continue
+			}
+			fields[fd.Name()] = Field{
+				Type:     dumpType(fd.Type()),
+				Embedded: fd.Embedded(),
+			}
+		}
+		dump["fields"] = fields
+		return dump
+	case *types.Slice:
+		dump["kind"] = "list"
+		dump["elem"] = dumpType(typ.Elem())
+		return dump
+	case *types.Pointer:
+		dump["kind"] = "pointer"
+		dump["elem"] = dumpType(typ.Elem())
+		return dump
+	case *types.Signature:
+		dump["kind"] = "function"
+		dump["params"] = dumpTuple(typ.Params())
+		dump["results"] = dumpTuple(typ.Results())
+		return dump
+	case *types.Basic:
+		return typ.String()
+	case *types.Named:
+		return typ.String()
+	}
+	panic("TODO: " + reflect.TypeOf(typ).String())
+}
+
+func dumpTuple(tuple *types.Tuple) []interface{} {
+	typs := make([]interface{}, 0)
+	for i := 0; i < tuple.Len(); i++ {
+		vr := tuple.At(i)
+		typs = append(typs, map[string]interface{}{
+			"name": vr.Name(),
+			"type": dumpType(vr.Type()),
+		})
+	}
+	return typs
+}