ErrLookup › PrefectHQ/fastmcp
PrefectHQ/fastmcp
🚀 The fast, Pythonic way to build MCP servers and clients. · Python · 282 source files
Analyzed at 1f02114297 on 2026-08-29. 461 documented errors.
| Code / Message | Type | Severity | Tags |
|---|---|---|---|
| Failed to resolve dependency | exception | error | dependency-injection, runtime, fastmcp |
| No active context found. This can happen if: - Called… | exception | error | context, asyncio, fastmcp |
| Failed to fetch JWKS | exception | error | network, ssrf, jwt, jwks |
invalid_grant Authorization code not found | error_code | error | oauth, token-exchange, invalid-grant |
| Failed to process JWKS | exception | error | jwt, jwks, configuration |
| response_title and response_description are only supported… | exception | error | elicitation, pydantic, schema, fastmcp |
INVALID_PARAMS server/discover result is not conformant with | error_code | warning | protocol, negotiation, mcp, client |
| Tool name collision | validation | error | mcp, naming-collision, client-group, configuration |
| FastMCP instance is no longer available | exception | error | python, lifecycle, weakref, garbage-collection |
| Unknown tool: . If servers changed their tools, call… | exception | error | mcp, client-group, unknown-tool, stale-cache |
| Cannot traverse part | exception | error | openapi, references, json-pointer |
| Assertion must include exp claim | exception | error | auth, jwt, oauth, identity-assertion |
| ClientGroup client for server | exception | error | mcp, connection, client-group, session-dropped |
| Assertion must include a string jti claim | validation | error | auth, oauth, jwt, identity-assertion |
| ClientGroup clients are not connected | exception | error | mcp, connection, client-group, async-context |
| Configuration file not found | exception | error | config, file-not-found, python |
| module has no attribute | exception | error | python, attributeerror, lazy-import |
| a custom cache store requires CacheConfig.target_id for… | validation | error | cache, configuration, validation, arguments |
| Invalid OpenAPI schema | validation | error | openapi, validation, schema |
| Cannot specify 'required_scopes' when providing a custom… | validation | error | python, configuration, oauth, constructor-validation |
| MethodBinding cannot bind spec method | exception | error | extensions, method-binding, api-misuse |
| Error rendering prompt | exception | error | prompts, error-handling, exception-wrapping |
| Failed to resolve reference | exception | error | openapi, json-ref, schema-resolution |
| Reference part ' ' not found in path | exception | error | openapi, references, json-pointer |
invalid_request invalid_request: Invalid redirect_uri. | error_code | error | oauth, redirect-uri, authorization |
| Key ID ' ' not found in JWKS | exception | error | auth, jwt, jwks, key-rotation |
| Expected fastmcp.server.auth.auth.AccessToken, got | exception | error | auth, type-mismatch, oauth |
| Missing client_assertion | http | error | oauth, authentication, jwt, client-assertion |
| Assertion replay detected: jti | validation | error | auth, oauth, replay-attack, jwt |
| ' ' uses a sync function but has task execution enabled… | validation | error | python, async, tasks, configuration |
| Error reading directory | exception | error | filesystem, resources, mcp-client |
| FastMCP server support is not installed. Install `fastmcp`… | exception | error | imports, installation, lazy-loading, optional-dependency |
| External or non-local reference not supported | exception | error | openapi, references, unsupported |
| Stateful proxy requires a per-connection server session; no… | exception | error | proxy, stateful, session, lifecycle |
| Claim ' ' not found in access token. Available claims | exception | error | auth, jwt, claims, fastmcp |
| [ ] Reached auto-pagination limit ( pages) for… | exception | error | pagination, client, mcp, runtime-error |
| CIMD documents cannot use shared-secret auth methods | validation | error | pydantic, cimd, validation, oauth-security |
| HTTP error | exception | error | http, openapi, upstream-api, network |
| ctx.elicit() requires a response_type. The empty-schema… | exception | error | elicitation, mcp, api-change, fastmcp |
| FormInput requires prefab-ui. Install with: pip install… | exception | error | dependency, optional-extra, import-error, prefab-ui |
| OAuth client not found - cached credentials may be stale | exception | error | oauth, auth, stale-credentials, client |
| Key ID ' ' found in JWKS but its key type is unsupported | exception | error | auth, jwt, jwks, key-type |
| Timeout fetching | exception | error | network, timeout, ssrf, dns, httpx |
| Authorization failed for prompt | exception | error | authorization, prompts, mcp |
| Component not found | exception | error | keyerror, provider, component-management |
| Elicitation schema field | exception | error | elicitation, schema-validation, json-schema |
| You must provide a name for lambda functions | validation | error | python, resources, naming |
| Unknown tool | exception | error | auth, authorization, tools, hashed-names |
| Authorization failed for resource | exception | error | auth, resources, middleware, access-control |
| Invalid cursor | exception | error | pagination, cursor, encoding |
| elicitation via server-initiated requests is unavailable on… | exception | error | python, context, elicitation, protocol-version, toolerror |
| cache_ttl must be a positive integer, got | validation | error | python, configuration, caching, valueerror |
| Imperative ctx.elicit() is not supported inside a… | exception | error | python, context, elicitation, background-tasks, toolerror |
| JWKS URI not configured | validation | error | auth, configuration, jwt, jwks |
| Error rendering prompt | exception | error | python, prompts, server |
| Invalid client_id | http | error | oauth, authentication, client-configuration |
| Failed to import from | exception | error | python, import, module-loading, plugin-discovery |
| No access token available. Cannot extract claim | exception | error | auth, claims, access-token, fastmcp |
| Unexpected elicitation action | exception | error | elicitation, protocol, mcp |
| HTTP request timed out | exception | error | network, http, timeout, openapi |
| URI template parameters | validation | error | uri-template, validation, naming |
| Could not restrict access to CLI state | exception | error | windows, permissions, filesystem, subprocess |
| External or non-local reference not supported | exception | error | openapi, external-ref, schema-bundling |
| File not found | exception | error | filesystem, file-not-found, resources, skills |
| contents[ ] must be ResourceContent, got . Use… | exception | error | python, resources, type-error |
| Error reading resource | exception | error | mcp, resource, error-masking, python |
| forward_raw() can only be called within a transformed tool | exception | error | python, tool-transform, context |
| Assertion resource does not match this server | validation | error | auth, oauth, resource-indicators, url-mismatch |
| No active HTTP request found. | exception | error | http, context, transport |
| Invalid token audience | validation | error | jwt, auth, audience-validation, configuration |
| Horizon returned an invalid organization cursor | exception | error | pagination, http, api |
| [ ] Reached auto-pagination limit ( pages) for… | exception | error | pagination, client, mcp, runtime-error |
| Authorization failed for tool | exception | error | auth, middleware, security, fail-closed |
| CIMD server returned 304 Not Modified without cached… | exception | error | oauth, cimd, http-cache, caching |
| ClientGroup is already connected | exception | error | python, async, lifecycle, reentrancy |
| Excluded headers must be lowercase | exception | warning | http, headers, validation |
| AzureProvider requires at least one non-OIDC scope in… | validation | error | python, azure, oauth, scopes, configuration |
| No image data available | validation | error | image, state, valueerror |
| Server overloaded, please retry | validation | error | auth, capacity, rate-limiting, replay-cache |
| At least one of version_gte or version_lt must be specified | validation | error | python, valueerror, version-filter, missing-argument, config |
| CIMD redirect_uri must have a host | validation | error | oauth, cimd, validation, redirect-uri |
| CIMD redirect_uri must have a scheme (e.g. http:// or… | validation | error | pydantic, cimd, validation, redirect-uri, url-parsing |
| OAuth server rejected the static client credentials. Verify… | exception | error | oauth, credentials, auth, configuration |
| Overall timeout exceeded | exception | error | network, timeout, ssrf, httpx |
| JWKS document contains no keys | exception | error | oauth, jwks, private-key-jwt, cimd |
| logging/setLevel is not available on MCP 2026-07-28… | exception | warning | python, logging, protocol, mcp |
| Remote server returned empty content for | exception | error | proxy, resource, empty-content, mcp |
| Error calling tool | exception | error | error-masking, tools, debugging |
| Expected a Prefab UI component | exception | error | prefab, ui, type-check |
| Task-enabled tools ( ) require the tasks extension, but no… | exception | error | tasks, extensions, startup, configuration |
| Unsupported content type | validation | error | anthropic, sampling, unsupported-content, valueerror |
| Version string cannot contain '@' (used as key delimiter) | exception | error | fastmcp, validation, versioning, key-format |
| Invalid client_assertion_type: expected | http | error | oauth, jwt, private-key-jwt, protocol-violation |
| Missing required configuration metadata | validation | error | oidc, configuration, discovery, validation |
| Assertion client_id does not match authenticated client | validation | error | auth, oauth, client-binding, identity-assertion |
| Assertion missing required scopes | validation | error | auth, oauth, scopes, identity-assertion |
| Authorization failed for resource | exception | error | auth, resources, middleware, fail-closed |
| Failed to sync dependencies | exception | error | uv, dependency-install, environment-setup, build |
| {str(e)} | validation | warning | validation, pydantic, arguments, client-error |
| structured_content must be a dict or None. Got | validation | error | python, valueerror, tool-result, structured-content, schema-validation |