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External MCP Catalogs

External MCP catalogs bring tools from another service into Flow Steward. This is different from the built-in Flow Steward MCP server, which exposes Flow Steward tools to external AI clients.

Add a catalog​

  1. Open Registry.
  2. Open MCP.
  3. Select Project scope. Connector credentials and projected tools belong to that project; + New MCP remains unavailable without it.
  4. Choose + New MCP, then enter the name and endpoint URL.
  5. Keep transport as streamable_http.
  6. Choose none, bearer, api_key, or oauth2 authentication. Add custom headers as separate key/value rows, not as a pasted JSON object.
  7. For OAuth, configure requested scopes and authorization parameters, start authorization, and complete the callback. Authorization, catalog sync, and health are separate states; a successful grant proves neither of the latter.
  8. Add a namespace prefix if tool names may collide, then save.
  9. Sync the complete paginated tools/list catalog and review excluded or malformed tools.
  10. Allowlist only discovered tools the project's workflows should call, then run health and a read-only test.

Credential-bearing endpoints must use HTTPS. Flow Steward rejects credentials in URLs/query strings, blocked local/private destinations under its SSRF policy, unsafe transport header annotations, malformed pages/cursors, and responses over 4 MiB. OAuth token expiry, missing refresh tokens, changed endpoint or credential revision, and scope expansion can require reconnect.

Operate safely​

  • Health-check the catalog before production use.
  • Review tool descriptions after every sync.
  • Use narrow credentials for the external service.
  • Keep dangerous tools out of the allowlist.
  • Run a test workflow before enabling broad use.
  • Remove or rotate credentials when the provider changes.