MCP Client Time out when adding specific POST Operation

Start by reproducing the /redact POST import in MCP Inspector with the supplied OpenAPI document. Then inspect the reported StreamableHTTP client and server paths in node_modules/@modelcontextprotocol/sdk/dist/esm/client/streamableHttp.js and server/streamableHttp.js alongside the timeout trace. Done means the imported operation completes without the SSE disconnect, HTTP 500 timeout, or missing request ID.

MCP Client Time out when adding specific POST Operation (/redact) Open API specification file at the end of the issue.

I am using MCP Inspector and this is the trace of the error:

Client <-> Proxy sessionId: <REDACTED_SESSION_ID>
Received POST message for sessionId <REDACTED_SESSION_ID>
Received GET message for sessionId <REDACTED_SESSION_ID>
Received POST message for sessionId <REDACTED_SESSION_ID>
Received POST message for sessionId <REDACTED_SESSION_ID>
Error from MCP server: Error: SSE stream disconnected: TypeError: terminated
at processStream (file:///.../node_modules/@modelcontextprotocol/sdk/dist/esm/client/streamableHttp.js:203:88)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
Error from MCP server: Error: Error POSTing to endpoint (HTTP 500): <title>500 - The request timed out.</title>

500 - The request timed out.

The web server failed to respond within the specified time.
at StreamableHTTPClientTransport.send (file:///.../node_modules/@modelcontextprotocol/sdk/dist/esm/client/streamableHttp.js:284:23)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
Error from inspector client: Error: No connection established for request ID: 1
at StreamableHTTPServerTransport.send (file:///.../node_modules/@modelcontextprotocol/sdk/dist/esm/server/streamableHttp.js:592:27)
at file:///.../node_modules/@modelcontextprotocol/inspector/server/build/mcpProxy.js:32:35
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)

Browser shows:
index-.js:23222 Uncaught (in promise) McpError: MCP error -32001: Request timed out
at timeoutHandler (index-.js:23222:43)

Open API json that I am using to import (just in case this is the source of problems)

{"openapi":"3.1.0","info":{"title":"Image PII Redactor API","version":"1.0.0"},"paths":{"/health":{"get":{"summary":"Health","operationId":"health_health_get","responses":{"200":{"description":"Successful Response","content":{"application/json":{"schema":{"additionalProperties":{"type":"string"},"type":"object","title":"Response Health Health Get"}}}}}}},"/config":{"get":{"summary":"Read Config","operationId":"read_config_config_get","responses":{"200":{"description":"Successful Response","content":{"application/json":{"schema":{"additionalProperties":true,"type":"object","title":"Response Read Config Config Get"}}}}}}},"/app-config.js":{"get":{"summary":"Runtime Config Js","description":"Serve a small JS snippet with runtime discoverable values.\n\nFrontend loads this before bootstrapping React. Keep it minimal to avoid\nadding latency. If additional config is needed, extend here.","operationId":"runtime_config_js_app_config_js_get","responses":{"200":{"description":"Successful Response","content":{"application/json":{"schema":{"type":"string","title":"Response Runtime Config Js App Config Js Get"}}}}}}},"/agent/settings":{"get":{"summary":"Read Agent Settings","description":"Return the current chat agent configuration variables.","operationId":"read_agent_settings_agent_settings_get","responses":{"200":{"description":"Successful Response","content":{"application/json":{"schema":{"$ref":"#/components/schemas/AgentSettingsResponse"}}}}}},"post":{"summary":"Update Agent Settings","description":"Persist chat agent configuration variables and restart the backend agent.","operationId":"update_agent_settings_agent_settings_post","requestBody":{"content":{"application/json":{"schema":{"$ref":"#/components/schemas/AgentSettingsUpdateRequest"}}},"required":true},"responses":{"200":{"description":"Successful Response","content":{"application/json":{"schema":{"$ref":"#/components/schemas/AgentSettingsResponse"}}}},"422":{"description":"Validation Error","content":{"application/json":{"schema":{"$ref":"#/components/schemas/HTTPValidationError"}}}}}}},"/redact":{"get":{"summary":"Describe Redact Endpoint","description":"Provide metadata so MCP/APIM clients can discover redact capabilities.","operationId":"describe_redact_endpoint_redact_get","responses":{"200":{"description":"Successful Response","content":{"application/json":{"schema":{"$ref":"#/components/schemas/RedactMetadataResponse"}}}}}},"post":{"tags":["mcp-tools"],"summary":"Redact PII entities from an image","description":"Redacts PII from a base64-encoded PNG/JPEG image. Provide fields such as analyzer, language, all_entities, selected_entities, fill_color, and debug. Returns a redacted image and metadata.","operationId":"redactImage","requestBody":{"content":{"application/json":{"schema":{"$ref":"#/components/schemas/RedactRequest","properties":{"image_base64":{"type":"string","description":"Base64 encoded PNG or JPEG image to redact."},"analyzer":{"type":"string","enum":["Local Analyzer","Azure AI Language","Local Analyzer + Azure AI Language"],"description":"Preferred analyzer backend. Defaults to automatic selection."},"language":{"type":"string","description":"ISO language code used for OCR and entity detection.","default":"en"},"all_entities":{"type":["string","boolean"],"description":"Set to false to limit redaction to selected_entities.","default":"true"},"selected_entities":{"items":{"type":"string"},"type":["array","null"],"description":"Subset of entity types to redact when all_entities is false."},"fill_color":{"type":"string","description":"Mask colour in hex format (default '#000000').","default":"#000000"},"debug":{"type":["string","boolean"],"description":"Enable verbose detection metadata (true/false).","default":"true"}},"type":"object","required":["image_base64"],"description":"Redaction parameters"},"example":{"image_base64":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUg...","analyzer":"Local Analyzer + Azure AI Language","language":"en","all_entities":"true","selected_entities":["EMAIL_ADDRESS","US_SOCIAL_SECURITY_NUMBER"],"fill_color":"#000000","debug":"false"}},"multipart/form-data":{"schema":{"properties":{"image_base64":{"type":"string","description":"Base64 encoded PNG/JPEG provided as form field."},"analyzer":{"type":"string"},"language":{"type":"string","default":"en"},"all_entities":{"type":"string","default":"true"},"selected_entities":{"type":"string","description":"JSON array string of entity types (required when all_entities=false)."},"fill_color":{"type":"string","default":"#000000"},"debug":{"type":"string","default":"true"}},"type":"object","required":["image_base64"]},"encoding":{"image_base64":{"contentType":"text/plain"},"selected_entities":{"contentType":"application/json"}}}},"required":true},"responses":{"200":{"description":"Successful Response","content":{"application/json":{"schema":{"additionalProperties":true,"type":"object","title":"Response Redactimage"}}}},"422":{"description":"Validation Error","content":{"application/json":{"schema":{"$ref":"#/components/schemas/HTTPValidationError"}}}}}},"options":{"summary":"Options Redact Endpoint","description":"Return CORS-friendly metadata for discovery clients.","operationId":"options_redact_endpoint_redact_options","responses":{"200":{"description":"Successful Response","content":{"application/json":{"schema":{}}}}}}},"/redact/metadata":{"get":{"tags":["mcp-tools"],"summary":"Describe Redact Endpoint Metadata","description":"MCP discovery endpoint for redact tool.\n\nProvides request schema and usage metadata so MCP/APIM clients\ncan correctly register and expose the redact tool.","operationId":"describe_redact_endpoint_metadata_redact_metadata_get","responses":{"200":{"description":"Successful Response","content":{"application/json":{"schema":{"$ref":"#/components/schemas/RedactMetadataResponse"}}}}}}},"/status":{"get":{"summary":"Status","description":"Expose runtime status for the UI (e.g. Azure availability).","operationId":"status_status_get","responses":{"200":{"description":"Successful Response","content":{"application/json":{"schema":{"additionalProperties":true,"type":"object","title":"Response Status Status Get"}}}}}}},"/agent/status":{"get":{"summary":"Agent Status","operationId":"agent_status_agent_status_get","responses":{"200":{"description":"Successful Response","content":{"application/json":{"schema":{"$ref":"#/components/schemas/AgentStatusResponse"}}}}}}},"/agent/chat":{"post":{"summary":"Agent Chat","operationId":"agent_chat_agent_chat_post","requestBody":{"content":{"application/json":{"schema":{"$ref":"#/components/schemas/AgentMessageRequest"}}},"required":true},"responses":{"200":{"description":"Successful Response","content":{"application/json":{"schema":{"$ref":"#/components/schemas/AgentMessageResponse"}}}},"422":{"description":"Validation Error","content":{"application/json":{"schema":{"$ref":"#/components/schemas/HTTPValidationError"}}}}}}}},"components":{"schemas":{"AgentAttachmentModel":{"properties":{"type":{"type":"string","title":"Type"},"data":{"type":"string","title":"Data"},"filename":{"anyOf":[{"type":"string"},{"type":"null"}],"title":"Filename"},"mime_type":{"anyOf":[{"type":"string"},{"type":"null"}],"title":"Mime Type"},"detail":{"anyOf":[{"type":"string"},{"type":"null"}],"title":"Detail"}},"type":"object","required":["type","data"],"title":"AgentAttachmentModel"},"AgentMessageRequest":{"properties":{"message":{"type":"string","minLength":1,"title":"Message"},"threadId":{"anyOf":[{"type":"string"},{"type":"null"}],"title":"Threadid"},"attachments":{"anyOf":[{"items":{"$ref":"#/components/schemas/AgentAttachmentModel"},"type":"array"},{"type":"null"}],"title":"Attachments"}},"type":"object","required":["message"],"title":"AgentMessageRequest","description":"Payload accepted by the /agent/chat endpoint."},"AgentMessageResponse":{"properties":{"agentId":{"type":"string","title":"Agentid"},"threadId":{"type":"string","title":"Threadid"},"runId":{"type":"string","title":"Runid"}},"type":"object","required":["agentId","threadId","runId"],"title":"AgentMessageResponse","description":"Structured response returned by the chat agent endpoint."},"AgentSettingsResponse":{"properties":{"variables":{"items":{"$ref":"#/components/schemas/AgentSettingsVariable"},"type":"array","title":"Variables"}},"type":"object","title":"AgentSettingsResponse"},"AgentSettingsUpdateItem":{"properties":{"key":{"type":"string","title":"Key"},"value":{"anyOf":[{"type":"string"},{"type":"null"}],"title":"Value"}},"additionalProperties":false,"type":"object","required":["key"],"title":"AgentSettingsUpdateItem"},"AgentSettingsUpdateRequest":{"properties":{"variables":{"items":{"$ref":"#/components/schemas/AgentSettingsUpdateItem"},"type":"array","title":"Variables"}},"type":"object","title":"AgentSettingsUpdateRequest"},"AgentSettingsVariable":{"properties":{"key":{"type":"string","title":"Key"},"label":{"type":"string","title":"Label"},"description":{"anyOf":[{"type":"string"},{"type":"null"}],"title":"Description"},"value":{"anyOf":[{"type":"string"},{"type":"null"}],"title":"Value"},"required":{"type":"boolean","title":"Required","default":false},"secret":{"type":"boolean","title":"Secret","default":false},"isSet":{"type":"boolean","title":"Isset","default":false}},"type":"object","required":["key","label"],"title":"AgentSettingsVariable"},"AgentStatusResponse":{"properties":{"ready":{"type":"boolean","title":"Ready"},"agent_id":{"anyOf":[{"type":"string"},{"type":"null"}],"title":"Agent Id"},"server_label":{"anyOf":[{"type":"string"},{"type":"null"}],"title":"Server Label"},"server_url":{"anyOf":[{"type":"string"},{"type":"null"}],"title":"Server Url"},"allowed_tools":{"items":{"type":"string"},"type":"array","title":"Allowed Tools","default":[]},"approval_mode":{"anyOf":[{"type":"string"},{"type":"null"}],"title":"Approval Mode"},"last_error":{"anyOf":[{"type":"string"},{"type":"null"}],"title":"Last Error"},"error":{"anyOf":[{"type":"string"},{"type":"null"}],"title":"Error"}},"type":"object","required":["ready"],"title":"AgentStatusResponse"},"HTTPValidationError":{"properties":{"detail":{"items":{"$ref":"#/components/schemas/ValidationError"},"type":"array","title":"Detail"}},"type":"object","title":"HTTPValidationError"},"RedactMetadataResponse":{"properties":{"method":{"type":"string","title":"Method","description":"HTTP verb used to submit redaction requests","default":"POST"},"description":{"type":"string","title":"Description","default":"Submit base64-encoded PNG/JPEG data and optional analyzer controls. See requestSchema for accepted fields."},"request_schema":{"additionalProperties":true,"type":"object","title":"Request Schema"}},"type":"object","title":"RedactMetadataResponse","description":"Describe how clients should interact with the redact endpoint."},"RedactRequest":{"properties":{"image_base64":{"type":"string","title":"Image Base64"},"analyzer":{"type":"string","title":"Analyzer","default":"Local Analyzer + Azure AI Language"},"language":{"type":"string","title":"Language","default":"en"},"all_entities":{"anyOf":[{"type":"string"},{"type":"boolean"}],"title":"All Entities","default":"true"},"selected_entities":{"anyOf":[{"items":{"type":"string"},"type":"array"},{"type":"null"}],"title":"Selected Entities"},"fill_color":{"type":"string","title":"Fill Color","default":"#000000"},"debug":{"anyOf":[{"type":"string"},{"type":"boolean"}],"title":"Debug","default":"true"}},"type":"object","required":["image_base64"],"title":"RedactRequest","description":"Incoming redaction request (tolerant of older/double-encoded clients).\n\nNotes:\n - Some callers (e.g. APIM test console) are sending the entire JSON body as a\n single serialized string. We unwrap that in a model-level validator.\n - "selected_entities" may arrive as a JSON string; we coerce it to a list.\n - Boolean-like fields arrive as strings; we keep them as str for existing\n downstream parsing but accept bools."},"ValidationError":{"properties":{"loc":{"items":{"anyOf":[{"type":"string"},{"type":"integer"}]},"type":"array","title":"Location"},"msg":{"type":"string","title":"Message"},"type":{"type":"string","title":"Error Type"}},"type":"object","required":["loc","msg","type"],"title":"ValidationError"}}}}