MCP JSON-RPC -32601 Method Not Found / Transport Handshake Mismatch

Legacy MCP clients sending raw GET requests to a Streamable-HTTP POST endpoint or calling tools/call before initialize receive JSON-RPC -32601 or 405 errors.

1. Immediate Code & SKU Fix

Replace With SKU: @modelcontextprotocol/sdk StreamableHTTPClientTransport

Install Command: npm install @modelcontextprotocol/sdk@latest

// POST JSON-RPC 2.0 {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26"}} to /api/mcp

2. Verified Hot-Swap Fallback Route

JTBD: mcp-hosting

Primary: mcp-registry → Fallback: cloudflare-workers

liveHealth: outage · autoActOk: true

Compliance blocks Anthropic

GET /api/rescue JSON (<2 KB)Falsify Pick (/api/falsify)

Matched Error String Signatures (5)

-32601Method not foundInvalid Request: MCP initializeMCP transport closed unexpectedlySSE endpoint deprecated

curl -s "https://getagentdepot.com/api/rescue?q=-32601"

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