diff --git a/tools/compliance/projectmetadata/projectmetadata.go b/tools/compliance/projectmetadata/projectmetadata.go
new file mode 100644
index 0000000..b31413d
--- /dev/null
+++ b/tools/compliance/projectmetadata/projectmetadata.go
@@ -0,0 +1,209 @@
+// Copyright 2022 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 projectmetadata
+
+import (
+	"fmt"
+	"io"
+	"io/fs"
+	"path/filepath"
+	"strings"
+	"sync"
+
+	"android/soong/compliance/project_metadata_proto"
+
+	"google.golang.org/protobuf/encoding/prototext"
+)
+
+var (
+	// ConcurrentReaders is the size of the task pool for limiting resource usage e.g. open files.
+	ConcurrentReaders = 5
+)
+
+// ProjectMetadata contains the METADATA for a git project.
+type ProjectMetadata struct {
+	proto project_metadata_proto.Metadata
+
+	// project is the path to the directory containing the METADATA file.
+	project string
+}
+
+// String returns a string representation of the metadata for error messages.
+func (pm *ProjectMetadata) String() string {
+	return fmt.Sprintf("project: %q\n%s", pm.project, pm.proto.String())
+}
+
+// VersionedName returns the name of the project including the version if any.
+func (pm *ProjectMetadata) VersionedName() string {
+	name := pm.proto.GetName()
+	if name != "" {
+		tp := pm.proto.GetThirdParty()
+		if tp != nil {
+			version := tp.GetVersion()
+			if version != "" {
+				if version[0] == 'v' || version[0] == 'V' {
+					return name + "_" + version
+				} else {
+					return name + "_v_" + version
+				}
+			}
+		}
+		return name
+	}
+	return pm.proto.GetDescription()
+}
+
+// projectIndex describes a project to be read; after `wg.Wait()`, will contain either
+// a `ProjectMetadata`, pm (can be nil even without error), or a non-nil `err`.
+type projectIndex struct {
+	project string
+	pm *ProjectMetadata
+	err error
+	done chan struct{}
+}
+
+// finish marks the task to read the `projectIndex` completed.
+func (pi *projectIndex) finish() {
+	close(pi.done)
+}
+
+// wait suspends execution until the `projectIndex` task completes.
+func (pi *projectIndex) wait() {
+	<-pi.done
+}
+
+// Index reads and caches ProjectMetadata (thread safe)
+type Index struct {
+	// projecs maps project name to a wait group if read has already started, and
+	// to a `ProjectMetadata` or to an `error` after the read completes.
+	projects sync.Map
+
+	// task provides a fixed-size task pool to limit concurrent open files etc.
+	task chan bool
+
+	// rootFS locates the root of the file system from which to read the files.
+	rootFS fs.FS
+}
+
+// NewIndex constructs a project metadata `Index` for the given file system.
+func NewIndex(rootFS fs.FS) *Index {
+	ix := &Index{task: make(chan bool, ConcurrentReaders), rootFS: rootFS}
+	for i := 0; i < ConcurrentReaders; i++ {
+		ix.task <- true
+	}
+	return ix
+}
+
+// MetadataForProjects returns 0..n ProjectMetadata for n `projects`, or an error.
+// Each project that has a METADATA.android or a METADATA file in the root of the project will have
+// a corresponding ProjectMetadata in the result. Projects with neither file get skipped. A nil
+// result with no error indicates none of the given `projects` has a METADATA file.
+// (thread safe -- can be called concurrently from multiple goroutines)
+func (ix *Index) MetadataForProjects(projects ...string) ([]*ProjectMetadata, error) {
+	if ConcurrentReaders < 1 {
+		return nil, fmt.Errorf("need at least one task in project metadata pool")
+	}
+	if len(projects) == 0 {
+		return nil, nil
+	}
+	// Identify the projects that have never been read
+	projectsToRead := make([]*projectIndex, 0, len(projects))
+	projectIndexes := make([]*projectIndex, 0, len(projects))
+	for _, p := range projects {
+		pi, loaded := ix.projects.LoadOrStore(p, &projectIndex{project: p, done: make(chan struct{})})
+		if !loaded {
+			projectsToRead = append(projectsToRead, pi.(*projectIndex))
+		}
+		projectIndexes = append(projectIndexes, pi.(*projectIndex))
+	}
+	// findMeta locates and reads the appropriate METADATA file, if any.
+	findMeta := func(pi *projectIndex) {
+		<-ix.task
+		defer func() {
+			ix.task <- true
+			pi.finish()
+		}()
+
+		// Support METADATA.android for projects that already have a different sort of METADATA file.
+		path := filepath.Join(pi.project, "METADATA.android")
+		fi, err := fs.Stat(ix.rootFS, path)
+		if err == nil {
+			if fi.Mode().IsRegular() {
+				ix.readMetadataFile(pi, path)
+				return
+			}
+		}
+		// No METADATA.android try METADATA file.
+		path = filepath.Join(pi.project, "METADATA")
+		fi, err = fs.Stat(ix.rootFS, path)
+		if err == nil {
+			if fi.Mode().IsRegular() {
+				ix.readMetadataFile(pi, path)
+				return
+			}
+		}
+		// no METADATA file exists -- leave nil and finish
+	}
+	// Look for the METADATA files to read, and record any missing.
+	for _, p := range projectsToRead {
+		go findMeta(p)
+	}
+	// Wait until all of the projects have been read.
+	var msg strings.Builder
+	result := make([]*ProjectMetadata, 0, len(projects))
+	for _, pi := range projectIndexes {
+		pi.wait()
+		// Combine any errors into a single error.
+		if pi.err != nil {
+			fmt.Fprintf(&msg, "  %v\n", pi.err)
+		} else if pi.pm != nil {
+			result = append(result, pi.pm)
+		}
+	}
+	if msg.Len() > 0 {
+		return nil, fmt.Errorf("error reading project(s):\n%s", msg.String())
+	}
+	if len(result) == 0 {
+		return nil, nil
+	}
+	return result, nil
+}
+
+// readMetadataFile tries to read and parse a METADATA file at `path` for `project`.
+func (ix *Index) readMetadataFile(pi *projectIndex, path string) {
+	f, err := ix.rootFS.Open(path)
+	if err != nil {
+		pi.err = fmt.Errorf("error opening project %q metadata %q: %w", pi.project, path, err)
+		return
+	}
+
+	// read the file
+	data, err := io.ReadAll(f)
+	if err != nil {
+		pi.err = fmt.Errorf("error reading project %q metadata %q: %w", pi.project, path, err)
+		return
+	}
+	f.Close()
+
+	uo := prototext.UnmarshalOptions{DiscardUnknown: true}
+	pm := &ProjectMetadata{project: pi.project}
+	err = uo.Unmarshal(data, &pm.proto)
+	if err != nil {
+		pi.err = fmt.Errorf("error in project %q metadata %q: %w", pi.project, path, err)
+		return
+	}
+
+	pi.pm = pm
+}