# MCP exception codes > The exception categories and codes that the MCP Access Exceptions report shows, with their messages [MCP Access Exceptions](/user-guide/audit-report/mcp/access-exceptions/) shows an exception category and an exception code for each row. This page lists every category and code that its **Category** and **Exception Code** filters offer, with the message that appears when you hover over a code. The report shows each category’s name and each code’s label. Each Workload Event records the same exception in `application.mcp.exceptionCategory` and `application.mcp.exceptionCode`, as the values in the following tables. For those fields, see [Supported protocols and application fields](/user-guide/audit-report/workload-events/supported-protocols/). ## Categories | Category | `exceptionCategory` value | | -------------------- | ------------------------- | | Access Policy | `ACCESS_POLICY` | | AIDR | `AIDR` | | Authorization Server | `AUTHORIZATION_SERVER` | | Bad Request | `BAD_REQUEST` | | Edge API | `EDGE_API` | | Elicitation | `ELICITATION` | | MCP Client | `MCP_CLIENT` | | MCP Gateway | `MCP_GATEWAY` | | MCP Server | `MCP_SERVER` | | Output Schema | `OUTPUT_SCHEMA` | | Tasks | `TASKS` | | Tool Filter | `TOOL_FILTER` | ## Exception codes Three codes appear in two categories, with a different message in each: `INTERNAL_ERROR`, `LISTEN_FAILED`, and `UNSUPPORTED_PROTOCOL_VERSION`. Read the category to tell them apart. Three codes have `Warning` severity: `CONFLICTING_RESOURCE_URI`, `AIDR_UNAVAILABLE_FAIL_OPEN_BYPASS`, and `UNSUPPORTED_METHOD`. Every other code has `Error` severity. | Category | Exception Code | `exceptionCode` value | Message | | -------------------- | --------------------------------- | ----------------------------------- | ------------------------------------------------------------------------------------ | | Access Policy | mTLS Over HTTP | `MTLS_OVER_HTTP` | `mTLS is configured, but the server workload accepts only HTTP.` | | Access Policy | Invalid Server Workload URL | `INVALID_SERVER_WORKLOAD_URL` | `Server workload service endpoint is not a valid URL.` | | Access Policy | Missing Service Endpoint | `MISSING_SERVICE_ENDPOINT` | `Server workload has no service endpoint configured.` | | Access Policy | Conflicting Workload Prefix | `CONFLICTING_WORKLOAD_PREFIX` | `Several assigned MCP servers share the same sanitized name prefix.` | | Access Policy | Conflicting Resource URI | `CONFLICTING_RESOURCE_URI` | `Several assigned MCP servers expose the same resource URI; the first one keeps it.` | | Access Policy | Credential Not Applicable | `CREDENTIAL_NOT_APPLICABLE` | `Credential provider configuration cannot be applied to the MCP server request.` | | AIDR | Tool Input Blocked | `TOOL_INPUT_BLOCKED` | `Tool call input was blocked by the AIDR policy.` | | AIDR | Tool Output Blocked | `TOOL_OUTPUT_BLOCKED` | `Tool call output was blocked by the AIDR policy.` | | AIDR | Tool Listing Blocked | `TOOL_LISTING_BLOCKED` | `Tool listing was blocked by the AIDR policy.` | | AIDR | AIDR Unavailable | `AIDR_UNAVAILABLE` | `AIDR service is unavailable: content was blocked (fail-closed).` | | AIDR | AIDR Unavailable Fail-Open Bypass | `AIDR_UNAVAILABLE_FAIL_OPEN_BYPASS` | `AIDR service is unavailable: content was passed through uninspected (fail-open).` | | Authorization Server | Missing Claims | `MISSING_CLAIMS` | `Access token is missing required claims.` | | Authorization Server | Invalid Claims | `INVALID_CLAIMS` | `Access token claims are not accepted.` | | Bad Request | Identifier Not Found | `IDENTIFIER_NOT_FOUND` | `Requested tool, prompt, resource, or task is not on any assigned MCP server.` | | Edge API | No MCP Servers Assigned | `NO_ASSIGNED_WORKLOADS` | `No MCP servers are assigned to this client.` | | Edge API | Missing Assessment Claims | `MISSING_ASSESSMENT_CLAIMS` | `Workload assessment is missing required claims.` | | Edge API | Internal Gateway Error | `INTERNAL_ERROR` | `Aembit Cloud failed to process the request.` | | Edge API | Subscription Listen Failed | `LISTEN_FAILED` | `Notification stream from Aembit Cloud failed.` | | Edge API | Credential Unavailable | `CREDENTIAL_UNAVAILABLE` | `Aembit Cloud could not provide credentials for the MCP server.` | | Elicitation | Elicitation Failed | `ELICITATION_FAILED` | `Elicitation request to the MCP client failed.` | | Elicitation | Input Rounds Exceeded | `INPUT_ROUNDS_EXCEEDED` | `MCP server requested input for more rounds than the gateway allows.` | | MCP Client | Invalid Audience | `INVALID_AUDIENCE` | `Access token audience does not match the gateway.` | | MCP Client | Malformed JSON-RPC Request | `MALFORMED_REQUEST` | `MCP client request is not a valid JSON-RPC message.` | | MCP Client | Invalid HTTP Request | `INVALID_HTTP_REQUEST` | `MCP client request violates the Streamable HTTP transport specification.` | | MCP Client | Host Not Allowed | `HOST_NOT_ALLOWED` | `Request Host or Origin header value is not allowed by the gateway.` | | MCP Client | Unsupported Protocol Version | `UNSUPPORTED_PROTOCOL_VERSION` | `MCP client requested an unsupported protocol version.` | | MCP Client | Missing Session ID | `MISSING_SESSION_ID` | `MCP session ID is missing.` | | MCP Client | Session Unavailable | `SESSION_UNAVAILABLE` | `MCP session was not found or has expired.` | | MCP Client | Client Terminated | `CLIENT_TERMINATED` | `MCP client closed the connection unexpectedly.` | | MCP Gateway | Internal Gateway Error | `INTERNAL_ERROR` | `MCP gateway failed to process the request.` | | MCP Gateway | Unsupported MCP Method | `UNSUPPORTED_METHOD` | `MCP method is not supported by the gateway.` | | MCP Server | Server Unreachable | `SERVER_UNREACHABLE` | `MCP server is unreachable.` | | MCP Server | Unsupported Protocol Version | `UNSUPPORTED_PROTOCOL_VERSION` | `MCP server supports no protocol version compatible with the gateway.` | | MCP Server | HTTP Error | `HTTP_ERROR` | `MCP server returned an HTTP error.` | | MCP Server | Redirect Refused | `REDIRECT_REFUSED` | `MCP server returned a redirect, which the gateway forbids.` | | MCP Server | Internal Destination Refused | `INTERNAL_DESTINATION_REFUSED` | `MCP server address resolves to an internal IP address, which the gateway forbids.` | | MCP Server | Malformed Response | `MALFORMED_RESPONSE` | `MCP server response is not a valid JSON-RPC message.` | | MCP Server | Server JSON-RPC Error | `JSONRPC_ERROR` | `MCP server returned a JSON-RPC error.` | | MCP Server | Timeout | `TIMEOUT` | `MCP server did not respond in time.` | | MCP Server | Capability Not Declared | `CAPABILITY_NOT_DECLARED` | `MCP server does not declare the capability the method requires.` | | MCP Server | Capability Not Implemented | `CAPABILITY_NOT_IMPLEMENTED` | `MCP server declares the capability but does not implement this method.` | | MCP Server | Tool Execution Failure | `TOOL_EXECUTION_FAILURE` | `Tool call returned an execution error.` | | MCP Server | Server Listen Failed | `LISTEN_FAILED` | `Notification stream from the MCP server failed.` | | MCP Server | Other Server Error | `OTHER` | `MCP server request failed.` | | Output Schema | Schema Violation | `SCHEMA_VIOLATION` | `Tool result does not match the declared output schema.` | | Tasks | Tasks Not Declared | `TASKS_NOT_DECLARED` | `MCP client called a task method without declaring the tasks capability.` | | Tasks | Unexpected Task Result | `UNEXPECTED_TASK_RESULT` | `MCP server returned a task result, but the MCP client does not support tasks.` | | Tool Filter | Tool Not Invocable | `TOOL_NOT_INVOCABLE` | `Tool call was blocked by the tool filter policy.` | | Tool Filter | Call Filter Failed | `CALL_FILTER_FAILED` | `Tool call was blocked: tool filter policy could not be evaluated.` | | Tool Filter | List Filter Failed | `LIST_FILTER_FAILED` | `Tool listing was blocked: tool filter policy could not be evaluated.` | ## Related pages * [MCP Access Exceptions](/user-guide/audit-report/mcp/access-exceptions/) * [Supported protocols and application fields](/user-guide/audit-report/workload-events/supported-protocols/)