diff --git a/main.go b/main.go
index a5248577..95581b62 100644
--- a/main.go
+++ b/main.go
@@ -3717,6 +3717,26 @@ func downloadAttachmentCmd(account *config.Account, uid uint32, folderName strin
 	}
 }
 
+// isLocalDevBuild reports whether this binary is an unstamped build running
+// outside of any package sandbox, e.g. `make build` or `go run .` from a
+// clone. It matters for the update checks: detectInstalledVersion falls back
+// to asking the system package manager, so a contributor running their own
+// build is told the version of the *packaged* Matcha they happen to have
+// installed, which almost never matches the latest release tag.
+//
+// Version alone isn't a reliable signal: snap and flatpak builds are also
+// unstamped (snapcraft.yaml and the flatpak manifest build without ldflags),
+// but they *are* managed by the update path (trySnapRefresh, tryFlatpakUpdate).
+// SNAP and FLATPAK_ID are always injected by their respective runtimes
+// (snapenv.basicEnv; flatpak-run.c's "FLATPAK_ID is always set"), so their
+// presence rules out a local dev build even when the version is unstamped.
+func isLocalDevBuild() bool {
+	v := strings.TrimSpace(version)
+	unstamped := v == "" || v == "dev"
+	sandboxed := os.Getenv("SNAP") != "" || os.Getenv("FLATPAK_ID") != ""
+	return unstamped && !sandboxed
+}
+
 /*
 detectInstalledVersion returns a best-effort installed version string.
 Priority:
@@ -3808,6 +3828,10 @@ installed version. This runs in the background when the TUI initializes.
 */
 func checkForUpdatesCmd() tea.Cmd {
 	return func() tea.Msg {
+		// A local dev build is not something `matcha update` can upgrade.
+		if isLocalDevBuild() {
+			return nil
+		}
 		// Non-fatal: if anything goes wrong we just don't show the update message.
 		const api = "https://api.github.com/repos/floatpane/matcha/releases/latest"
 		resp, err := httpClient.Get(api)
@@ -3834,6 +3858,10 @@ func checkForUpdatesCmd() tea.Cmd {
 // a V1RCAvailableMsg when the installed version is still pre-v1.
 func checkForV1RCCmd() tea.Cmd {
 	return func() tea.Msg {
+		// Same reasoning as checkForUpdatesCmd.
+		if isLocalDevBuild() {
+			return nil
+		}
 		const api = "https://api.github.com/repos/floatpane/matcha/releases"
 		resp, err := httpClient.Get(api)
 		if err != nil {
diff --git a/main_test.go b/main_test.go
index e698f416..03e9d0e4 100644
--- a/main_test.go
+++ b/main_test.go
@@ -171,6 +171,60 @@ func TestUndoDeleteRestoresFolderCounter(t *testing.T) {
 	}
 }
 
+func TestIsLocalDevBuildDetectsUnstampedVersions(t *testing.T) {
+	original := version
+	t.Cleanup(func() { version = original })
+
+	for _, tc := range []struct {
+		name    string
+		version string
+		snap    string
+		flatpak string
+		want    bool
+	}{
+		{name: "plain go build", version: "dev", want: true},
+		{name: "empty ldflags value", version: "", want: true},
+		{name: "whitespace only", version: "  ", want: true},
+		{name: "released version", version: "0.44.0", want: false},
+		{name: "tagged version", version: "v1.0.0-rc1", want: false},
+		{name: "unstamped snap build", version: "dev", snap: "/snap/matcha/42", want: false},
+		{name: "unstamped flatpak build", version: "dev", flatpak: "com.floatpane.matcha", want: false},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			version = tc.version
+			// An empty value stands in for "unset": isLocalDevBuild compares
+			// against "", so absent and set-but-empty are equivalent. Setting
+			// both also isolates the test from a runner that is itself inside a
+			// snap or flatpak.
+			t.Setenv("SNAP", tc.snap)
+			t.Setenv("FLATPAK_ID", tc.flatpak)
+
+			if got := isLocalDevBuild(); got != tc.want {
+				t.Fatalf("isLocalDevBuild() with version %q, SNAP=%q, FLATPAK_ID=%q = %t, want %t",
+					tc.version, tc.snap, tc.flatpak, got, tc.want)
+			}
+		})
+	}
+}
+
+func TestUpdateChecksAreSkippedOnLocalDevBuilds(t *testing.T) {
+	original := version
+	t.Cleanup(func() { version = original })
+	version = "dev"
+	t.Setenv("SNAP", "")
+	t.Setenv("FLATPAK_ID", "")
+
+	// Both checks must bail out before reaching the GitHub API, so a dev build
+	// neither advertises an update nor makes a network call to find one.
+	if msg := checkForUpdatesCmd()(); msg != nil {
+		t.Fatalf("checkForUpdatesCmd() on a dev build = %#v, want nil", msg)
+	}
+
+	if msg := checkForV1RCCmd()(); msg != nil {
+		t.Fatalf("checkForV1RCCmd() on a dev build = %#v, want nil", msg)
+	}
+}
+
 func TestUnreadBadgeCountDeduplicatesOverlappingStores(t *testing.T) {
 	email := fetcher.Email{UID: 42, AccountID: "acct-a"}
 	got := unreadBadgeCount(