PrefectHQ/fastmcp
Documented errors, page 2 of 5. Back to PrefectHQ/fastmcp
| Code / Message | Type | Severity | Tags |
|---|---|---|---|
| The client negotiated a modern protocol era… | exception | error | python, protocol, mcp, api-migration |
| Invalid client assertion | http | error | oauth, jwt, signature-validation, cimd |
| Response too large: bytes (max ) | exception | error | network, ssrf, size-limit, http |
| Session task completed without exception but connection… | exception | error | python, transport, startup, race-condition |
| $defs collision for ' ': an ArgTransform introduces a… | validation | error | python, schema, tool-transform, json-schema |
| Elicitation responses must be serializable as a JSON object… | validation | error | python, elicitation, validation, json |
| {str(e) from SSRFError/SSRFFetchError} | exception | error | oauth, cimd, ssrf, network, security |
| Invalid JWKS JSON | exception | error | json, http, jwt, jwks |
| Invalid path | validation | error | path-traversal, security, skill-provider, validation |
| No authorization response stored. redirect_handler must be… | exception | error | oauth, testing, auth, flow-order |
| Ambiguous app tool : components share the identity . The… | exception | error | proxy, tool-routing, duplicate-registration, ambiguity |
| Error listing directory | exception | error | filesystem, permissions, resources, glob |
| Missing required arguments | exception | error | prompts, validation, arguments |
| Invalid CIMD document | validation | error | oauth, cimd, pydantic, schema-validation |
| FastMCP server instance is no longer available | exception | error | context, lifecycle, garbage-collection |
| OIDC discovery for issuer | exception | warning | network, oidc, discovery, retry, backoff |
| Authorization failed for tool | exception | error | auth, tools, middleware, access-control |
| Invalid token issuer | validation | error | jwt, auth, issuer-validation, configuration |
| No FastMCP server instance in context | exception | error | context, server, lifecycle |
| OBO token exchange requires either a client_secret or a… | validation | error | python, azure, obo, credentials, configuration |
| [ ] Reached auto-pagination limit ( pages) for list_tools… | exception | error | pagination, client, mcp, runtime-error |
| Directory not found | exception | error | filesystem, resources, path-not-found |
| Protocol mode for server | validation | error | python, type-error, configuration, validation |
| Subclasses must implement create_resource(). Use… | exception | error | python, resource-templates, not-implemented |
| Invalid JWT assertion | exception | error | oauth, cimd, jwt, private-key-jwt, authentication |
| No access token found. Ensure authentication is configured… | exception | error | auth, oauth, access-token, fastmcp |
unsupported_grant_type unsupported_grant_type: The JWT bearer grant is not supported by this… | error_code | error | oauth, id-jag, jwt-bearer, unsupported-grant-type |
| Client must have CIMD document for private_key_jwt | exception | error | oauth, cimd, private-key-jwt, client-metadata |
| mcp_tool() got unexpected keyword argument(s) | exception | error | python, decorator, type-error, fastmcp |
| Unexpected CreateTaskResult: Context calls should not have… | exception | error | python, context, prompts, internal-error, runtimeerror |
| Assertion failed signature/issuer/audience/expiry validation | exception | error | jwt, signature, expired, audience, security |
| request_id is not available because the MCP session has not… | exception | error | python, context, request-id, runtimeerror, session-lifecycle |
| tenant_name should be the short name without the… | validation | error | python, azure, azure-ad-b2c, configuration |
| Component keys are missing the '@' version delimiter and… | console | warning | python, transforms, component-keys, filtering |
| \nOriginal error | exception | error | asgi, runtime-error, deployment |
| No active context found. | exception | error | context, lifecycle, request-scope |
| str(e) | exception | error | oauth, cimd, network, http |
| Authorization failed for prompt | exception | error | authorization, oauth-scopes, prompts |
| Could not extract project_id from config_url | validation | error | python, descope, oauth, configuration, url-parsing |
| Functions with *args are not supported as resource templates | validation | error | python, resources, signature |
| Task group is not initialized. Make sure to use run(). | exception | critical | asgi, lifespan, deployment |
| Token type mismatch: expected | validation | error | jwt, auth, token-validation |
| Unexpected authorization response | exception | error | oauth, http, authorization-server, network |
| app-bridge.js not found in ext-apps tarball | exception | error | packaging, tarball, upstream-drift, npm |
| Either high_entropy_material or low_entropy_material must… | exception | error | configuration, missing-env-var, jwt-signing, cryptography |
| Elicitation schema field | exception | error | elicitation, json-schema, refs, fastmcp |
| Rate limited by upstream API, please retry later | exception | warning | rate-limit, http-429, tools, retry |
| Skill name would escape the target directory | validation | error | security, path-traversal, skills |
| Progress dependency requires a FastMCP server context. | exception | error | progress, context, fastmcp |
| Provided resource URI is invalid | validation | error | uri, validation, client, resources, valueerror |
| A completion handler returned a str; return a list of… | exception | error | python, completions, typeerror, return-type |
| Authorization failed for prompt | exception | error | authorization, prompts, access-control |
| Authorization failed for prompt | exception | error | auth, prompts, middleware, fail-closed |
| Authorization failed for tool | exception | error | auth, oauth, scopes, jwt, insufficient-scope |
| CIMD documents must include at least one redirect_uri | validation | error | pydantic, cimd, validation, redirect-uri |
| OIDC discovery for issuer | exception | error | network, oidc, discovery, http |
| Authorization failed for tool | exception | error | auth, middleware, access-control, custom-auth |
| Error fetching | exception | error | network, tls, ssrf, httpx, connection |
| Multiple keys in JWKS but no key ID (kid) in token | exception | error | auth, jwt, jwks, kid |
| Server failed to start after | exception | error | testing, server-startup, timeout, subprocess |
| Value for state key is not serializable. Use set_state( … | exception | error | state, serialization, pydantic |
| jwt_signing_key is required when upstream_client_secret is… | exception | critical | oauth, jwt, configuration, startup |
| Assertion claim must be a number | validation | error | jwt, validation, timestamp, auth |
| CIMD jwks_uri failed SSRF validation | validation | error | oauth, cimd, ssrf, security, jwks |
| No value is valid against a false schema | validation | error | json-schema, validation, pydantic |
| Setting does not exist. | exception | error | python, attributeerror, settings, nested-attribute, typo |
| Error fetching : no fetch targets succeeded | exception | error | network, ssrf, dns, edge-case |
| Expected integer, got | validation | error | validation, cli, input-parsing, integer |
| Invalid JSON in tool arguments for | exception | error | openai, sampling, json, tool-calls, truncation |
invalid_target Resource does not match this server | error_code | error | oauth, rfc-8707, resource-indicator, audience |
| Invalid URL | exception | error | config, url, validation, mcp |
| No keys found in JWKS | exception | error | auth, jwt, jwks, configuration |
| ToolTransform has duplicate target name | validation | error | python, valueerror, tool-transform, duplicate-name, config |
| Invalid list response_type format. Received | exception | error | elicitation, schema, fastmcp, python |
| Either high_entropy_material or low_entropy_material must… | exception | error | configuration, cryptography, jwt-signing |
| ImageContent is only supported in user messages for OpenAI | validation | error | openai, sampling, multimodal, validation |
| MCP configs that use FastMCP-specific tool transforms or… | exception | error | import, installation, dependency, mcp |
| Elicitation response missing required 'value' field. | exception | error | elicitation, response-validation, fastmcp, mcp-client |
invalid_redirect_uri Redirect URI ' ' is not allowed. | error_code | error | oauth, dcr, redirect-uri, registration |
| Token has expired | validation | error | jwt, auth, token-expired |
| OAuth provider has no server URL. Either pass mcp_url to… | exception | error | oauth, configuration, misuse, client |
| To decorate a classmethod, use @classmethod above @prompt… | exception | error | prompts, decorator, classmethod, typeerror |
| contents must be str, bytes, or list[ResourceContent], got | exception | error | python, resources, type-error |
| Could not read manifest for skill | exception | error | skills, mcp-resources, manifest |
| Failed to initialize project | exception | error | environment, uv, subprocess, project-init |
| cache_ttl_seconds must be non-negative, got | validation | error | validation, configuration, valueerror |
| CLI state is invalid | validation | error | json, validation, corruption, state |
| Subclasses must implement render() | exception | error | prompts, not-implemented, subclassing, python |
| User server did not start on port | exception | error | network, startup, timeout, dev-server, port |
408 Timed out while waiting for response. | error_code | error | network, timeout, httpx, client |
| Assertion must include sub claim | validation | error | auth, jwt, oauth, identity-assertion |
| Cannot resolve tool reference | exception | error | python, valueerror, tool-registration |
| Either config_url (new API) or both project_id and… | validation | error | configuration, oauth, constructor |
| Function missing parameters required after transformation | validation | error | python, tool-transform, signature-mismatch |
| Hidden parameter ' ' has no default value in parent tool… | validation | error | python, tool-transform, validation |
| Malformed assertion header | exception | error | jwt, malformed, parsing |
| meta['fastmcp'] must be a dict | exception | error | fastmcp, validation, metadata, type-error |
| Pattern is not supported by Pydantic's regex engine and… | console | warning | python, json-schema, regex, pydantic, validation |
| Assertion is not yet valid (nbf in future) | exception | error | auth, jwt, clock-skew, identity-assertion |
| client_id is required for client registration | exception | error | oauth, dcr, client-registration, validation |