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MCP · Specification

Answer what the MCP specification requires: the exact JSON-RPC request and response shapes for every method, error codes, how a client and server agree on a protocol version, capabilities, and which behaviours are MUST rather than SHOULD.

629 notes · updated 2026-08-04 · trained 57%

since last sitting: +17 newly passed — this brain is learning

Ask it things like

answers 16/28 on its latest exam · anti-bluff 1/2
The _meta field in request must carry which three pieces of information for proper handshake?Handshake & Version Negotiation✓
A client wants to negotiate protocol version 2026-07-28. Where does it place this value and what header must the server also send?Handshake & Version Negotiation✓
When should a tool error like 'file not found' be placed in a CallToolResult vs a JSON-RPC error response?JSON-RPC Envelope & Error Codes✓
When a client subscribes via subscriptions/listen, what MUST be the first message it receives?Subscriptions & Notifications✓
What information MUST a server include in DiscoverResult.supportedVersions and when does the client use it?Handshake & Version Negotiation✓
What is the exact shape of an elicitation/create request and what two modes does it support?Input-Required & Elicitation✓
What must resultType be set to when a server's resource/read response requires user input before fetching?JSON-RPC Envelope & Error Codes✓
How does a client cancel an in-flight request, and what constraint applies to the requestId?Lifecycle, Cancellation & Progress✓
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$ claude mcp add --transport http mozg \
https://mozg.sh/mcp --header "Authorization: Bearer …"
> use mozg/mcp-spec — …
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What it can answer

28 checks
57%
▲Handshake & Version Negotiation3 / 4
✓Subscriptions & Notifications3 / 3
▲Transport & HTTP Binding3 / 4
▲Input-Required & Elicitation2 / 4
▲JSON-RPC Envelope & Error Codes2 / 5
✓Lifecycle, Cancellation & Progress2 / 2
▲Capabilities & Feature Flags1 / 2
✕Methods & Request/Response Shapes0 / 4
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Inside

  • JSONRPCNotification shape (no id) · json-rpc envelope & error codes
  • ElicitResult action semantics: accept, decline, cancel · input-required
  • JSONRPCMessage union: request, notification, response · json-rpc envelope & error codes
  • JSONRPCRequest shape · json-rpc envelope & error codes
  • JSONRPCResultResponse shape · json-rpc envelope & error codes
  • JSONRPCErrorResponse shape has optional id · json-rpc envelope & error codes
  • TextContent shape · tools, resources, prompts method shapes
  • Acknowledged `notifications` filter omits unsupported types · subscriptions
  • name vs title display precedence · tools, resources, prompts method shapes
  • resources/list request shape (ListResourcesRequest) · tools, resources, prompts method shapes
  • ListResourcesResult fields · tools, resources, prompts method shapes
  • nextCursor pagination token semantics · tools, resources, prompts method shapes
  • PromptArgument fields · tools, resources, prompts method shapes
  • Error object fields: code, message, data · json-rpc envelope & error codes

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