github/github-mcp-server · warning

failed to marshal labels: %w

Error message

failed to marshal labels: %w

What it means

json.Marshal of the labels response map ([]labels, totalCount, has_more) failed. The map holds only GraphQL-derived strings and ints, so a marshal error indicates unsupported values (NaN floats sneaking in) or upstream githubv4 type changes - effectively unreachable in a healthy build.

Source

Thrown at pkg/github/ui_tools.go:175

		if !query.Repository.Labels.PageInfo.HasNextPage {
			break
		}
		if page >= uiGetMaxPages {
			hasMore = true
			break
		}
		vars["cursor"] = githubv4.NewString(query.Repository.Labels.PageInfo.EndCursor)
	}

	response := map[string]any{
		"labels":     labels,
		"totalCount": totalCount,
		"has_more":   hasMore,
	}

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

	return utils.NewToolResultText(string(out)), nil, nil
}

func uiGetAssignees(ctx context.Context, deps ToolDependencies, args map[string]any, owner string) (*mcp.CallToolResult, any, error) {
	repo, err := RequiredParam[string](args, "repo")
	if err != nil {
		return utils.NewToolResultError(err.Error()), nil, nil
	}

	client, err := deps.GetClient(ctx)
	if err != nil {
		return utils.NewToolResultErrorFromErr("failed to get GitHub client", err), nil, nil
	}

	opts := &github.ListOptions{PerPage: 100}
	var allAssignees []*github.User

View on GitHub (pinned to 0ea1f775a7)

Solutions

1. Log the underlying marshal error to find the offending field
2. Pin the githubv4 version matching this server build
3. Add a unit test marshaling a sample labels response map

out, err := json.Marshal(response)
if err != nil {
	slog.Error("marshal labels failed", "error", err)
	out = []byte(`{"labels":[],"totalCount":0,"has_more":false}`)
}

When it happens

Trigger: githubv4 dependency drift changing node field types; injecting non-marshalable values into the map in a fork.

Common situations: Version skew after upgrading githubv4; local modifications to uiGetLabels.

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/2ed44a66323eef0b. Report an issue: GitHub.