What causes "loading post-renderer result: %w" in GoogleContainerTools/skaffold?

Run the post-renderer manually on the same stdin and inspect its output

loading post-renderer result: %w

Error message

loading post-renderer result: %w

What it means

Wraps a failure from manifest.Load(stdoutPipe) when parsing the output of the post-renderer process. It indicates the post-renderer ran but produced output Skaffold cannot parse as Kubernetes manifests.

Source

Thrown at cmd/skaffold/app/cmd/filter.go:87

func runFilter(ctx context.Context, out io.Writer, debuggingFilters bool, postRenderer string, buildArtifacts []graph.Artifact) error {
	return withRunner(ctx, out, func(r runner.Runner, configs []util.VersionedConfig) error {
		var manifestList manifest.ManifestList
		var err error
		if postRenderer != "" {
			cmd := exec.CommandContext(ctx, postRenderer)
			cmd.Stdin = os.Stdin
			stdoutPipe, err := cmd.StdoutPipe()
			if err != nil {
				return fmt.Errorf("running post-renderer: %w", err)
			}
			err = cmd.Start()
			if err != nil {
				return fmt.Errorf("running post-renderer: %w", err)
			}

			manifestList, err = manifest.Load(stdoutPipe)
			if err != nil {
				return fmt.Errorf("loading post-renderer result: %w", err)
			}
			stdoutPipe.Close()
		} else {
			manifestList, err = manifest.Load(os.Stdin)
		}
		if err != nil {
			return fmt.Errorf("loading manifests: %w", err)
		}
		var ass applysetters.ApplySetters
		manifestOverrides := pkgutil.EnvSliceToMap(opts.ManifestsOverrides, "=")
		for k, v := range manifestOverrides {
			ass.Setters = append(ass.Setters, applysetters.Setter{Name: k, Value: v})
		}
		manifestList, err = ass.Apply(ctx, manifestList)
		if err != nil {
			return err
		}
		allow, deny := getTransformList(configs)

View on GitHub (pinned to a1189de023)

Solutions

Run the post-renderer manually on the same stdin and inspect its output
Silence or redirect any non-manifest logging the post-renderer emits to stdout
Ensure the post-renderer exits 0 and emits only valid YAML manifests
Check the wrapped error for the parse failure location

Example fix

// before: post-renderer prints banners to stdout
# my-post-renderer.sh
echo "processing..."
filter_output
// after: log to stderr only
# my-post-renderer.sh
echo "processing..." >&2
filter_output

Defensive patterns

Strategy: validation

Validate before calling

// test the post-renderer before piping into skaffold
out, err := exec.Command(postRenderer).Input(stdinBytes).Output()
if err != nil || len(out) == 0 {
    return fmt.Errorf("post-renderer produced no/invalid output")
}

Try / catch

if err != nil {
    return fmt.Errorf("loading post-renderer result: %w", err)
}

Prevention

Post-renderer must write only YAML manifests to stdout
Send logs/diagnostics to stderr
Verify the post-renderer exits non-zero on failure so errors are not parsed as manifests

When it happens

Trigger: --post-renderer is set, cmd.Start() succeeded, and manifest.Load(stdoutPipe) fails (invalid YAML, empty output, post-renderer wrote errors/diagnostics to stdout), wrapped at filter.go:87.

Common situations: Post-renderer emits non-manifest text (logs, progress), exits early producing truncated YAML, or outputs a format Skaffold's manifest parser rejects.

Related errors

AI-assisted analysis of GoogleContainerTools/skaffold@a1189de023 (2026-09-05). Data as JSON: /api/errors/e46d32b502ca7b69. Report an issue: GitHub.