Fixing MCP failure detector: false positives traced to SDK error code overloading
Thirumalaiboobathi · reddit · 2026-08-03
A developer shares the process of fixing a false positive in their MCP failure detector. Community feedback pointed out that detection logic missed JSON-RPC error objects (-32601/-32602), and the SDK converts most protocol errors to isError: true, but -32602 is overloaded across four conditions in the TypeScript SDK: tool not found, tool disabled, input validation failure, and output validation failure. Output validation failures are server-side schema bugs and should not be counted as agent retry thrash. v0.7.0 fixes this by excluding output validation failures and adding per-channel thresholds. The author also found that fingerprint hashing already discriminates field-level convergence, so regression tests were added.
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