github/github-mcp-server · info

failed to marshal label: %w

Error message

failed to marshal label: %w

What it means

The get_label tool failed to JSON-encode the label map built from GraphQL results (id, name, color, description — all strings). Marshal errors are effectively impossible for this shape; the guard exists for safety and signals an internal serialization bug if ever hit.

Source

Thrown at pkg/github/labels.go:111

			if err := client.Query(ctx, &query, vars); err != nil {
				return ghErrors.NewGitHubGraphQLErrorResponse(ctx, "Failed to find label", err), nil, nil
			}

			if query.Repository.Label.Name == "" {
				return utils.NewToolResultError(fmt.Sprintf("label '%s' not found in %s/%s", name, owner, repo)), nil, nil
			}

			label := map[string]any{
				"id":          fmt.Sprintf("%v", query.Repository.Label.ID),
				"name":        string(query.Repository.Label.Name),
				"color":       string(query.Repository.Label.Color),
				"description": string(query.Repository.Label.Description),
			}

			out, err := json.Marshal(label)
			if err != nil {
				return nil, nil, fmt.Errorf("failed to marshal label: %w", err)
			}

			result := utils.NewToolResultText(string(out))
			// Labels are structural repo metadata defined by collaborators
			// (trusted); confidentiality follows repo visibility.
			result = attachRepoVisibilityIFCLabelLazy(ctx, deps, owner, repo, result, ifc.LabelRepoMetadata)
			return result, nil, nil
		},
	)
}

// GetLabelForLabelsToolset returns the same GetLabel tool but registered in the labels toolset.
// This provides conformance with the original behavior where get_label was in both toolsets.
func GetLabelForLabelsToolset(t translations.TranslationHelperFunc) inventory.ServerTool {
	tool := GetLabel(t)
	tool.Toolset = ToolsetLabels
	return tool
}

View on GitHub (pinned to 0ea1f775a7)

Solutions

1. Treat as an internal bug: report the github-mcp-server version and label data involved
2. Retry once to rule out a transient anomaly; the label query itself already succeeded

if err != nil && strings.Contains(err.Error(), "failed to marshal label") {
    // Internal serialization bug; the label lookup succeeded. File an issue with the version.
}

When it happens

Trigger: Not reproducible through the API with the current string-only map; would require the map values to become unsupported types via a code change.

Common situations: Essentially never seen; if reported, it follows a server modification of the label map structure.

Related errors

• failed to marshal labels: %w
• GitHub App authentication and GITHUB_PERSONAL_ACCESS_TOKEN a
• GitHub App ID or client ID is required (GITHUB_APP_ID)
• repo is required
• failed to marshal response: %w

AI-assisted analysis of github/github-mcp-server@0ea1f775a7 (2026-08-15). Data as JSON: /api/errors/a8212b797599563f. Report an issue: GitHub.