diff --git a/internal/labels/labeler.go b/internal/labels/labeler.go
index a18a315..eba0c07 100644
--- a/internal/labels/labeler.go
+++ b/internal/labels/labeler.go
@@ -88,6 +88,102 @@ func (l *Labeler) RequireApproval() {
 	l.requireApproval = true
 }
 
+// Run runs a single round of labeling to GitHub.
+// It scans all open issues that have been created since the last call to [Labeler.Run]
+// using a Labeler with the same name (see [New]).
+// TODO(jba): more doc
+func (l *Labeler) Run(ctx context.Context) error {
+	l.slog.Info("labels.Labeler start", "name", l.name, "label", l.label, "latest", l.watcher.Latest())
+	defer func() {
+		l.slog.Info("labels.Labeler end", "name", l.name, "latest", l.watcher.Latest())
+	}()
+
+	// Ensure that labels in GH match our config.
+	for p := range l.projects {
+		if err := l.syncLabels(ctx, p); err != nil {
+			return err
+		}
+	}
+	// TODO(jba): finish implementation.
+	return nil
+}
+
+func (l *Labeler) syncLabels(ctx context.Context, project string) error {
+	// TODO(jba): generalize to other projects.
+	if project != "golang/go" {
+		return errors.New("labeling only supported for golang/go")
+	}
+	l.slog.Info("syncing labels", "name", l.name, "project", project)
+	return syncLabels(ctx, l.slog, config.Categories, ghLabels{l.github, project})
+}
+
+// trackerLabels manipulates the set of labels on an issue tracker.
+// TODO: remove dependence on GitHub.
+type trackerLabels interface {
+	CreateLabel(ctx context.Context, lab github.Label) error
+	EditLabel(ctx context.Context, name string, changes github.LabelChanges) error
+	ListLabels(ctx context.Context) ([]github.Label, error)
+}
+
+type ghLabels struct {
+	gh      *github.Client
+	project string
+}
+
+func (g ghLabels) CreateLabel(ctx context.Context, lab github.Label) error {
+	return g.gh.CreateLabel(ctx, g.project, lab)
+}
+
+func (g ghLabels) EditLabel(ctx context.Context, name string, changes github.LabelChanges) error {
+	return g.gh.EditLabel(ctx, g.project, name, changes)
+}
+
+func (g ghLabels) ListLabels(ctx context.Context) ([]github.Label, error) {
+	return g.gh.ListLabels(ctx, g.project)
+}
+
+// labelColor is the color of labels created by syncLabels.
+const labelColor = "4d0070"
+
+// syncLabels attempts to reconcile the labels in cats with the labels on the issue tracker,
+// modifying the issue tracker's labels to match.
+// If a label in cats is not on the issue tracker, it is created.
+// Otherwise, if the label description on the issue tracker is empty, it is set to the description in the Category.
+// Otherwise, if the descriptions don't agree, a warning is logged and nothing is done on the issue tracker.
+// This function makes no other changes. In particular, it never deletes labels.
+func syncLabels(ctx context.Context, lg *slog.Logger, cats []Category, tl trackerLabels) error {
+	tlabList, err := tl.ListLabels(ctx)
+	if err != nil {
+		return err
+	}
+	tlabs := map[string]github.Label{}
+	for _, lab := range tlabList {
+		tlabs[lab.Name] = lab
+	}
+
+	for _, cat := range cats {
+		lab, ok := tlabs[cat.Label]
+		if !ok {
+			lg.Info("creating label", "label", lab.Name)
+			if err := tl.CreateLabel(ctx, github.Label{
+				Name:        cat.Label,
+				Description: cat.Description,
+				Color:       labelColor,
+			}); err != nil {
+				return err
+			}
+		} else if lab.Description == "" {
+			lg.Info("setting empty label description", "label", lab.Name)
+			if err := tl.EditLabel(ctx, lab.Name, github.LabelChanges{Description: cat.Description}); err != nil {
+				return err
+			}
+		} else if lab.Description != cat.Description {
+			lg.Warn("descriptions disagree", "label", lab.Name)
+		}
+	}
+	return nil
+}
+
 type actioner struct {
 	l *Labeler
 }
diff --git a/internal/labels/labeler_test.go b/internal/labels/labeler_test.go
new file mode 100644
index 0000000..a0f3f06
--- /dev/null
+++ b/internal/labels/labeler_test.go
@@ -0,0 +1,77 @@
+// Copyright 2024 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 labels
+
+import (
+	"context"
+	"errors"
+	"maps"
+	"slices"
+	"testing"
+
+	"golang.org/x/oscar/internal/github"
+	"golang.org/x/oscar/internal/testutil"
+)
+
+func TestSyncLabels(t *testing.T) {
+	m := map[string]github.Label{
+		"A": {Name: "A", Description: "a", Color: "a"},
+		"B": {Name: "B", Description: "", Color: "b"},
+		"C": {Name: "C", Description: "c", Color: "c"},
+		"D": {Name: "D", Description: "d", Color: "d"},
+	}
+	cats := []Category{
+		{Label: "A", Description: "a"},     // same as tracker
+		{Label: "B", Description: "b"},     // set empty tracker description
+		{Label: "C", Description: "other"}, // different descriptions
+		// D in tracker but not in cats
+		{Label: "E", Description: "e"}, // create
+	}
+	tl := &testTrackerLabels{m}
+
+	if err := syncLabels(context.Background(), testutil.Slogger(t), cats, tl); err != nil {
+		t.Fatal(err)
+	}
+
+	want := map[string]github.Label{
+		"A": {Name: "A", Description: "a", Color: "a"},
+		"B": {Name: "B", Description: "b", Color: "b"}, // added B description
+		"C": {Name: "C", Description: "c", Color: "c"},
+		"D": {Name: "D", Description: "d", Color: "d"},
+		"E": {Name: "E", Description: "e", Color: labelColor}, // added E
+	}
+
+	if got := tl.m; !maps.Equal(got, want) {
+		t.Errorf("\ngot  %v\nwant %v", got, want)
+	}
+}
+
+type testTrackerLabels struct {
+	m map[string]github.Label
+}
+
+func (t *testTrackerLabels) CreateLabel(ctx context.Context, lab github.Label) error {
+	if _, ok := t.m[lab.Name]; ok {
+		return errors.New("label exists")
+	}
+	t.m[lab.Name] = lab
+	return nil
+}
+
+func (t *testTrackerLabels) ListLabels(ctx context.Context) ([]github.Label, error) {
+	return slices.Collect(maps.Values(t.m)), nil
+}
+
+func (t *testTrackerLabels) EditLabel(ctx context.Context, name string, changes github.LabelChanges) error {
+	if changes.NewName != "" || changes.Color != "" {
+		return errors.New("unsupported edit")
+	}
+	if lab, ok := t.m[name]; ok {
+		lab.Description = changes.Description
+		t.m[name] = lab
+		return nil
+	}
+	return errors.New("not found")
+}
diff --git a/internal/labels/static/categories.yaml b/internal/labels/static/categories.yaml
index 7ca595d..a2b3155 100644
--- a/internal/labels/static/categories.yaml
+++ b/internal/labels/static/categories.yaml
@@ -7,11 +7,11 @@
 #         with the description
 categories:
   - name: bug
-    label: BUGLABEL
+    label: Bug
     description: "Issues describing a bug in the Go implementation."
 
   - name: languageProposal
-    label: LANGPROPLABEL
+    label: LanguageProposal
     description: Issues describing a requested change to the Go language specification.
     extra: |
       This should be used for any notable change or addition to the language.
@@ -20,7 +20,7 @@ categories:
       changes in existing functionality.
 
   - name: libraryProposal
-    label: LIBPROPLABEL
+    label: LibraryProposal
     description: Issues describing a requested change to the Go standard library or x/ libraries, but not to a tool
     extra: |
       This should be used for any notable change or addition to the libraries.
@@ -33,7 +33,7 @@ categories:
       and probably a GODEBUG setting.
 
   - name: toolProposal
-    label: TOOLPROPLABEL
+    label: ToolProposal
     description: Issues describing a requested change to a Go tool or command-line program.
     extra: |
       This should be used for any notable change or addition to the tools.
@@ -47,11 +47,11 @@ categories:
       This does NOT includ changes to tools in x repos, like gopls, or third-party tools.
 
   - name: implementation
-    label: IMPLABEL
+    label: Implementation
     description: Issues describing a semantics-preserving change to the Go implementation.
 
   - name: accessRequest
-    label: accessRequestLABEL
+    label: AccessRequest
     description: Issues requesting builder or gomote access.
 
   - name: pkgsiteRemovalRequest
@@ -60,11 +60,11 @@ categories:
     # We don't label issues posted by gopherbot, so this label is probably unnecessary.
 
   - name: automation
-    label: automationLABEL
+    label: Automation
     description: Issues created by gopherbot or watchflakes automation.
 
   - name: backport
-    label: backportLABEL
+    label: Backport
     description: Issues created for requesting a backport of a change to a previous Go version.
 
   - name: builders
@@ -72,7 +72,7 @@ categories:
     description: x/build issues (builders, bots, dashboards)
 
   - name: question
-    label: questionLABEL
+    label: Question
     description: Issues that are questions about using Go.
     # It may be too challenging for the LLM to decide is something is WAI. Consider removing this.
 
@@ -81,7 +81,7 @@ categories:
     description: Issues describing something that is working as it is supposed to.
 
   - name: featureRequest
-    label: FeatureRequestLABEL
+    label: FeatureRequest
     description: Issues asking for a new feature that does not need a proposal.
 
   - name: documentation
@@ -90,10 +90,10 @@ categories:
     # The LLM never seems to pick invalid.
 
   - name: invalid
-    label: invalidLABEL
+    label: Invalid
     description: Issues that are empty, incomplete, or spam.
     # The LLM never seems to pick other.
 
   - name: other
-    label: otherLABEL
+    label: Other
     description: None of the above.