github/github-mcp-server · info

failed to marshal response: %w

Error message

failed to marshal response: %w

What it means

Returned by listProjects when json.Marshal fails on the response map containing minimalProjects and pageInfo. The MinimalProject values are plain structs of strings, ints, pointers, and time.Time — all JSON-serializable — so in practice this error is near-unreachable; it exists to satisfy error handling. If it ever fires, a struct field of an unmarshalable type (chan, func, complex, or a marshal-time error from a custom MarshalJSON) is the cause.

Source

Thrown at pkg/github/projects.go:1109

	// For specified owner_type, process normally
	if ownerType != "" {
		defer func() { _ = resp.Body.Close() }()

		for _, project := range projects {
			mp := convertToMinimalProject(project)
			mp.OwnerType = ownerType
			minimalProjects = append(minimalProjects, *mp)
		}

		response := map[string]any{
			"projects": minimalProjects,
			"pageInfo": buildPageInfo(resp),
		}

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

		return utils.NewToolResultText(string(r)), projectVisibilities(minimalProjects), nil, nil
	}

	return nil, nil, nil, fmt.Errorf("unexpected state in listProjects")
}

// listProjectsFromBothOwnerTypes fetches projects from both user and org endpoints
// when owner_type is not specified, combining the results with owner_type labels.
func listProjectsFromBothOwnerTypes(ctx context.Context, client *github.Client, owner string, opts *github.ListProjectsOptions) (*mcp.CallToolResult, []bool, any, error) {
	var minimalProjects []MinimalProject
	var resp *github.Response

	// Fetch user projects
	userProjects, userResp, userErr := client.Projects.ListUserProjects(ctx, owner, opts)
	if userErr == nil && userResp.StatusCode == http.StatusOK {
		for _, project := range userProjects {

View on GitHub (pinned to 0ea1f775a7)

Solutions

1. If you are a server contributor: check the failing struct for func/chan/complex fields or custom MarshalJSON methods and fix the type
2. As a tool caller: capture the full error (it wraps the json error with type details) and report it as a server-side bug; retrying with different arguments will not help
3. Pin/upgrade to a released server version where the regression is not present
4. If NaN/Inf may enter floats, sanitize them before they reach the response struct

result, vis, resp, err := listProjects(ctx, client, owner, opts)
if err != nil {
    if errors.Is(err, errJSONMarshalPrefix) || strings.Contains(err.Error(), "failed to marshal response") {
        // internal serialization defect: do not retry; capture server version and report
        reportServerBug(err)
        return err
    }
    return err
}

When it happens

Trigger: A MinimalProject field gaining a chan/func/complex type or a custom MarshalJSON that returns an error; unsupported NaN/Inf in a float field (json.Marshal rejects those); a cyclic pointer structure introduced by refactoring.

Common situations: Contributors extending MinimalProject with non-serializable fields during feature work; embedding time values that a custom marshaller chokes on for zero dates. End users essentially never see this from argument input.

Related errors

• 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
• failed to marshal workflow: %w

AI-assisted analysis of github/github-mcp-server@0ea1f775a7 (2026-08-15). Data as JSON: /api/errors/d8ffde68b61c7305. Report an issue: GitHub.