github/github-mcp-server · info

unsupported ref type: %s

Error message

unsupported ref type: %s

What it means

CompleteRequest.Params.Ref.Type is neither ref/prompt nor ref/resource. The MCP spec defines exactly those two ref shapes for completion; any other string (typo, future ref type, custom value) lands in the default branch and is rejected.

Source

Thrown at pkg/github/server.go:206

	return s
}

func CompletionsHandler(getClient GetClientFn) func(ctx context.Context, req *mcp.CompleteRequest) (*mcp.CompleteResult, error) {
	return func(ctx context.Context, req *mcp.CompleteRequest) (*mcp.CompleteResult, error) {
		if req == nil || req.Params == nil || req.Params.Ref == nil {
			return nil, fmt.Errorf("missing required parameter: ref")
		}
		switch req.Params.Ref.Type {
		case "ref/resource":
			if strings.HasPrefix(req.Params.Ref.URI, "repo://") {
				return RepositoryResourceCompletionHandler(getClient)(ctx, req)
			}
			return nil, fmt.Errorf("unsupported resource URI: %s", req.Params.Ref.URI)
		case "ref/prompt":
			return nil, nil
		default:
			return nil, fmt.Errorf("unsupported ref type: %s", req.Params.Ref.Type)
		}
	}
}

func MarshalledTextResult(v any) *mcp.CallToolResult {
	data, err := json.Marshal(v)
	if err != nil {
		return utils.NewToolResultErrorFromErr("failed to marshal text result to json", err)
	}

	return utils.NewToolResultText(string(data))
}

View on GitHub (pinned to 0ea1f775a7)

Solutions

1. Send only ref/prompt (with name) or ref/resource (with uri) refs
2. Align client and server MCP protocol versions
3. Handle the error client-side by skipping completion for that ref

function isSupportedRefType(t string) boolean {
	return t === "ref/prompt" || t === "ref/resource";
}

When it happens

Trigger: Client sends ref/type=ref/tool or a custom string; newer MCP spec adds a ref type this server version does not know (version skew); handcrafted JSON requests.

Common situations: Client/server version drift after MCP spec additions; exploratory tooling probing the completion endpoint.

Related errors

• missing required parameter: ref
• App not connected
• failed to get repositories
• owner or repo not specified
• failed to get file tree

AI-assisted analysis of github/github-mcp-server@0ea1f775a7 (2026-08-15). Data as JSON: /api/errors/57ae627991d6eece. Report an issue: GitHub.