ComposioHQ/composio · error · ValidationError

Failed to parse MCP server instance

Error message

Failed to parse MCP server instance

What it means

A catch-all wrapper around the whole MCP.generate() body: any exception that is not already a ValidationError (e.g. AttributeError while building the MCPServerInstance dict, KeyError on server_details fields, JSON issues) is re-raised as 'Failed to parse MCP server instance'. Pre-existing ValidationErrors pass through untouched.

Source

Thrown at python/composio/core/models/mcp.py:500

                raise ValidationError("No server URL generated")

            # Create structured server instance (matching TS MCPServerInstance)
            server_instance: MCPServerInstance = {
                "id": server_details.id,
                "name": server_details.name,
                "type": "streamable_http",
                "url": server_url,
                "user_id": user_id,
                "allowed_tools": getattr(server_details, "allowed_tools", []),
                "auth_configs": getattr(server_details, "auth_config_ids", []),
            }

            return server_instance

        except Exception as e:
            if isinstance(e, ValidationError):
                raise
            raise ValidationError("Failed to parse MCP server instance") from e

View on GitHub (pinned to 64b1b85502)

Solutions

1. Inspect e.__cause__ to see the exact AttributeError/KeyError and which field was missing
2. Upgrade (or pin) composio to the version whose generated client matches the backend
3. Retry once to rule out transient partial responses

try:
    inst = composio.mcp.create(...)
except ValidationError as e:
    logger.error('parse failed: %r', e.__cause__)
    raise

When it happens

Trigger: The generate flow succeeds at HTTP level but the response object is missing expected attributes (server_details.id, server_details.name) or the URL parsing step raises — usually generated-client/backend schema drift.

Common situations: Old composio version against a new backend, or vice versa; backend returning an error object where a server config was expected.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Failed to fetch file from URL: {_sanitize_url_for_logging(ur
• File size ({content_length} bytes) exceeds maximum allowed s
• Failed to list MCP servers
• Failed to retrieve MCP server {server_id}
• Failed to update MCP server {server_id}

AI-assisted analysis of ComposioHQ/composio@64b1b85502 (2026-08-28). Data as JSON: /api/errors/92fbfba5a5c92670. Report an issue: GitHub.