diff --git a/api/internal/crawl/cmd/crawler/crawler.go b/api/internal/crawl/cmd/crawler/crawler.go
index 4a7883e54..2d301efe1 100644
--- a/api/internal/crawl/cmd/crawler/crawler.go
+++ b/api/internal/crawl/cmd/crawler/crawler.go
@@ -9,6 +9,8 @@ import (
 	"os"
 	"time"
 
+	"sigs.k8s.io/kustomize/api/internal/crawl/utils"
+
 	"sigs.k8s.io/kustomize/api/internal/crawl/crawler"
 	"sigs.k8s.io/kustomize/api/internal/crawl/crawler/github"
 	"sigs.k8s.io/kustomize/api/internal/crawl/doc"
@@ -26,6 +28,7 @@ const (
 )
 
 type CrawlMode int
+
 const (
 	CrawlUnknown CrawlMode = iota
 	// Crawl all the kustomization files in all the repositories of a Github user
@@ -125,13 +128,13 @@ func main() {
 
 	// seen tracks the IDs of all the documents in the index.
 	// This helps avoid indexing a given document multiple times.
-	seen := crawler.NewSeenMap()
+	seen := utils.NewSeenMap()
 
 	mode := NewCrawlMode(*modePtr)
 
 	ghCrawlerConstructor := func(user, repo string) crawler.Crawler {
 		if user != "" {
-			return 	github.NewCrawler(githubToken, retryCount, clientCache,
+			return github.NewCrawler(githubToken, retryCount, clientCache,
 				github.QueryWith(
 					github.Filename("kustomization.yaml"),
 					github.Filename("kustomization.yml"),
diff --git a/api/internal/crawl/cmd/kustomize_stats/main.go b/api/internal/crawl/cmd/kustomize_stats/main.go
index 234d1327c..d3a436ebe 100644
--- a/api/internal/crawl/cmd/kustomize_stats/main.go
+++ b/api/internal/crawl/cmd/kustomize_stats/main.go
@@ -7,7 +7,6 @@ import (
 	"log"
 	"net/http"
 	"os"
-	"sigs.k8s.io/kustomize/api/internal/crawl/crawler"
 	"sort"
 	"time"
 
@@ -51,10 +50,10 @@ func GeneratorAndTransformerStats(ctx context.Context,
 	generatorDocs []*doc.Document, transformerDocs []*doc.Document,
 	idx *index.KustomizeIndex) {
 	// allGenerators includes all the documents referred in the generators field
-	allGenerators := crawler.NewUniqueDocuments()
+	allGenerators := doc.NewUniqueDocuments()
 
 	// allTransformers includes all the documents referred in the transformers field
-	allTransformers := crawler.NewUniqueDocuments()
+	allTransformers := doc.NewUniqueDocuments()
 
 	// docUsingGeneratorCount counts the number of the kustomization files using generators
 	docUsingGeneratorCount := 0
diff --git a/api/internal/crawl/crawler/crawler.go b/api/internal/crawl/crawler/crawler.go
index 2f7026e7a..11715616d 100644
--- a/api/internal/crawl/crawler/crawler.go
+++ b/api/internal/crawl/crawler/crawler.go
@@ -10,6 +10,8 @@ import (
 	"os"
 	"sync"
 
+	"sigs.k8s.io/kustomize/api/internal/crawl/utils"
+
 	"sigs.k8s.io/kustomize/api/internal/crawl/index"
 
 	_ "github.com/gomodule/redigo/redis"
@@ -29,7 +31,7 @@ type Crawler interface {
 	// Crawl returns when it is done processing. This method does not take
 	// ownership of the channel. The channel is write only, and it
 	// designates where the crawler should forward the documents.
-	Crawl(ctx context.Context, output chan<- CrawledDocument, seen SeenMap) error
+	Crawl(ctx context.Context, output chan<- CrawledDocument, seen utils.SeenMap) error
 
 	// Get the document data given the FilePath, Repo, and Ref/Tag/Branch.
 	FetchDocument(context.Context, *doc.Document) error
@@ -52,21 +54,6 @@ type CrawledDocument interface {
 	WasCached() bool
 }
 
-type SeenMap map[string]struct{}
-
-func (seen SeenMap) Seen(item string) bool {
-	_, ok := seen[item]
-	return ok
-}
-
-func (seen SeenMap) Add(item string) {
-	seen[item] = struct{}{}
-}
-
-func NewSeenMap() SeenMap {
-	return make(map[string]struct{})
-}
-
 type CrawlSeed []*doc.Document
 
 type IndexFunc func(CrawledDocument, index.Mode) error
@@ -89,7 +76,7 @@ func findMatch(d *doc.Document, crawlers []Crawler) Crawler {
 }
 
 func addBranches(cdoc CrawledDocument, match Crawler, indx IndexFunc,
-	seen SeenMap, stack *CrawlSeed) {
+	seen utils.SeenMap, stack *CrawlSeed) {
 
 	seen.Add(cdoc.ID())
 
@@ -115,7 +102,7 @@ func addBranches(cdoc CrawledDocument, match Crawler, indx IndexFunc,
 }
 
 func doCrawl(ctx context.Context, docsPtr *CrawlSeed, crawlers []Crawler, conv Converter, indx IndexFunc,
-	seen SeenMap, stack *CrawlSeed) {
+	seen utils.SeenMap, stack *CrawlSeed) {
 
 	UpdatedDocCount := 0
 	seenDocCount := 0
@@ -166,7 +153,6 @@ func doCrawl(ctx context.Context, docsPtr *CrawlSeed, crawlers []Crawler, conv C
 		// `bases` field.
 		seen.Add(tail.ID())
 
-
 		if err := match.FetchDocument(ctx, tail); err != nil {
 			logger.Printf("FetchDocument failed on doc(%s): %v", tail.Path(), err)
 			FetchDocumentErrCount++
@@ -212,7 +198,7 @@ func doCrawl(ctx context.Context, docsPtr *CrawlSeed, crawlers []Crawler, conv C
 // CrawlFromSeed updates all the documents in seed, and crawls all the new
 // documents referred in the seed.
 func CrawlFromSeed(ctx context.Context, seed CrawlSeed, crawlers []Crawler,
-	conv Converter, indx IndexFunc, seen SeenMap) {
+	conv Converter, indx IndexFunc, seen utils.SeenMap) {
 
 	// stack tracks the documents directly referred in other documents.
 	stack := make(CrawlSeed, 0)
@@ -248,7 +234,7 @@ func CrawlFromSeed(ctx context.Context, seed CrawlSeed, crawlers []Crawler,
 // from the seed will be processed before any other documents from the
 // crawlers.
 func CrawlGithubRunner(ctx context.Context, output chan<- CrawledDocument,
-	crawlers []Crawler, seen SeenMap) []error {
+	crawlers []Crawler, seen utils.SeenMap) []error {
 
 	errs := make([]error, len(crawlers))
 	wg := sync.WaitGroup{}
@@ -292,7 +278,7 @@ func CrawlGithubRunner(ctx context.Context, output chan<- CrawledDocument,
 
 // CrawlGithub crawls all the kustomization files on Github.
 func CrawlGithub(ctx context.Context, crawlers []Crawler, conv Converter,
-	indx IndexFunc, seen SeenMap) {
+	indx IndexFunc, seen utils.SeenMap) {
 	// stack tracks the documents directly referred in other documents.
 	stack := make(CrawlSeed, 0)
 
diff --git a/api/internal/crawl/crawler/crawler_test.go b/api/internal/crawl/crawler/crawler_test.go
index 7dace4da6..d18a4afce 100644
--- a/api/internal/crawl/crawler/crawler_test.go
+++ b/api/internal/crawl/crawler/crawler_test.go
@@ -12,6 +12,8 @@ import (
 	"testing"
 	"time"
 
+	"sigs.k8s.io/kustomize/api/internal/crawl/utils"
+
 	"sigs.k8s.io/kustomize/api/internal/crawl/index"
 
 	"sigs.k8s.io/kustomize/api/internal/crawl/doc"
@@ -76,7 +78,7 @@ func newCrawler(matchPrefix string, err error,
 
 // Crawl implements the Crawler interface for testing.
 func (c testCrawler) Crawl(_ context.Context,
-	output chan<- CrawledDocument, _ SeenMap) error {
+	output chan<- CrawledDocument, _ utils.SeenMap) error {
 
 	for i, d := range c.docs {
 		isResource := true
@@ -182,7 +184,7 @@ func TestCrawlGithubRunner(t *testing.T) {
 			defer close(output)
 			defer wg.Done()
 
-			seen := NewSeenMap()
+			seen := utils.NewSeenMap()
 			errs := CrawlGithubRunner(context.Background(),
 				output, test.tc, seen)
 
@@ -324,7 +326,7 @@ resources:
 				visited[d.ID()]++
 				return nil
 			},
-			NewSeenMap(),
+			utils.NewSeenMap(),
 		)
 		if lv, lc := len(visited), len(tc.corpus); lv != lc {
 			t.Errorf("error: %d of %d documents visited.", lv, lc)
diff --git a/api/internal/crawl/crawler/github/crawler.go b/api/internal/crawl/crawler/github/crawler.go
index 046ba4af0..e1aeff401 100644
--- a/api/internal/crawl/crawler/github/crawler.go
+++ b/api/internal/crawl/crawler/github/crawler.go
@@ -16,6 +16,8 @@ import (
 	"strings"
 	"time"
 
+	"sigs.k8s.io/kustomize/api/internal/crawl/utils"
+
 	"sigs.k8s.io/kustomize/api/internal/crawl/crawler"
 	"sigs.k8s.io/kustomize/api/internal/crawl/doc"
 	"sigs.k8s.io/kustomize/api/internal/crawl/httpclient"
@@ -68,7 +70,7 @@ func (gc githubCrawler) DefaultBranch(repo string) string {
 
 // Implements crawler.Crawler.
 func (gc githubCrawler) Crawl(ctx context.Context,
-	output chan<- crawler.CrawledDocument, seen crawler.SeenMap) error {
+	output chan<- crawler.CrawledDocument, seen utils.SeenMap) error {
 
 	noETagClient := GhClient{
 		RequestConfig: gc.client.RequestConfig,
@@ -195,9 +197,9 @@ func (gc githubCrawler) Match(d *doc.Document) bool {
 
 type RangeQueryResult struct {
 	totalDocCnt uint64
-	seenDocCnt   uint64
-	newDocCnt uint64
-	errorCnt  uint64
+	seenDocCnt  uint64
+	newDocCnt   uint64
+	errorCnt    uint64
 }
 
 func (r *RangeQueryResult) Add(other RangeQueryResult) {
@@ -209,7 +211,7 @@ func (r *RangeQueryResult) Add(other RangeQueryResult) {
 
 func (r *RangeQueryResult) String() string {
 	return fmt.Sprintf("got %d files from API. "+
-		"%d have been seen before. %d are new and sent to the output channel." +
+		"%d have been seen before. %d are new and sent to the output channel."+
 		" %d have kustomizationResultAdapter errors.",
 		r.totalDocCnt, r.seenDocCnt, r.newDocCnt, r.errorCnt)
 }
@@ -217,7 +219,7 @@ func (r *RangeQueryResult) String() string {
 // processQuery follows all of the pages in a query, and updates/adds the
 // documents from the crawl to the datastore/index.
 func processQuery(ctx context.Context, gcl GhClient, query string,
-	output chan<- crawler.CrawledDocument, seen crawler.SeenMap,
+	output chan<- crawler.CrawledDocument, seen utils.SeenMap,
 	branchMap map[string]string) (RangeQueryResult, error) {
 
 	queryPages := make(chan GhResponseInfo)
@@ -271,7 +273,7 @@ func processQuery(ctx context.Context, gcl GhClient, query string,
 	return result, errs
 }
 
-func kustomizationResultAdapter(gcl GhClient, k GhFileSpec, seen crawler.SeenMap,
+func kustomizationResultAdapter(gcl GhClient, k GhFileSpec, seen utils.SeenMap,
 	branchMap map[string]string) (crawler.CrawledDocument, error) {
 	url := gcl.ReposRequest(k.Repository.FullName)
 	defaultBranch, err := gcl.GetDefaultBranch(url, k.Repository.URL, branchMap)
diff --git a/api/internal/crawl/crawler/github/queries.go b/api/internal/crawl/crawler/github/queries.go
index 557e0f371..ba05af38f 100644
--- a/api/internal/crawl/crawler/github/queries.go
+++ b/api/internal/crawl/crawler/github/queries.go
@@ -117,7 +117,7 @@ type RequestConfig struct {
 // understand why the request object is useful.
 func (rc RequestConfig) CodeSearchRequestWith(query Query) request {
 	vals := url.Values{
-		"sort": []string{"indexed"},
+		"sort":  []string{"indexed"},
 		"order": []string{"desc"},
 	}
 	req := rc.makeRequest("search/code", query, vals)
diff --git a/api/internal/crawl/doc/docname_test.go b/api/internal/crawl/doc/docname_test.go
index f1b65dc8f..a03beaf06 100644
--- a/api/internal/crawl/doc/docname_test.go
+++ b/api/internal/crawl/doc/docname_test.go
@@ -65,7 +65,7 @@ func TestFromRelativePath(t *testing.T) {
 
 func TestDocument_RepositoryFullName(t *testing.T) {
 	testCases := []struct {
-		doc Document
+		doc                        Document
 		expectedRepositoryFullName string
 	}{
 		{
@@ -108,4 +108,4 @@ func TestDocument_RepositoryFullName(t *testing.T) {
 				returnedRepositoryFullName)
 		}
 	}
-}
\ No newline at end of file
+}
diff --git a/api/internal/crawl/doc/unique_doc.go b/api/internal/crawl/doc/unique_doc.go
new file mode 100644
index 000000000..026b345a5
--- /dev/null
+++ b/api/internal/crawl/doc/unique_doc.go
@@ -0,0 +1,36 @@
+package doc
+
+import (
+	"sigs.k8s.io/kustomize/api/internal/crawl/utils"
+)
+
+// UniqueDocuments make sure a Document with a given ID appears only once
+type UniqueDocuments struct {
+	docs   []*Document
+	docIDs utils.SeenMap
+}
+
+func NewUniqueDocuments() UniqueDocuments {
+	return UniqueDocuments{
+		docs:   []*Document{},
+		docIDs: utils.NewSeenMap(),
+	}
+}
+
+func (uds *UniqueDocuments) Add(d *Document) {
+	if uds.docIDs.Seen(d.ID()) {
+		return
+	}
+	uds.docs = append(uds.docs, d)
+	uds.docIDs.Add(d.ID())
+}
+
+func (uds *UniqueDocuments) AddDocuments(docs []*Document) {
+	for _, d := range docs {
+		uds.Add(d)
+	}
+}
+
+func (uds *UniqueDocuments) Documents() []*Document {
+	return uds.docs
+}
diff --git a/api/internal/crawl/index/kustomize.go b/api/internal/crawl/index/kustomize.go
index e55c5547e..7e2e7b104 100644
--- a/api/internal/crawl/index/kustomize.go
+++ b/api/internal/crawl/index/kustomize.go
@@ -18,6 +18,7 @@ const (
 )
 
 type Mode int
+
 const (
 	InsertOrUpdate = iota
 	Delete
diff --git a/api/internal/crawl/utils/utils.go b/api/internal/crawl/utils/utils.go
new file mode 100644
index 000000000..a397b2d52
--- /dev/null
+++ b/api/internal/crawl/utils/utils.go
@@ -0,0 +1,16 @@
+package utils
+
+type SeenMap map[string]struct{}
+
+func (seen SeenMap) Seen(item string) bool {
+	_, ok := seen[item]
+	return ok
+}
+
+func (seen SeenMap) Add(item string) {
+	seen[item] = struct{}{}
+}
+
+func NewSeenMap() SeenMap {
+	return make(map[string]struct{})
+}