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Claude Desktop rejects tool despite passing all validation tests

A developer encountered an issue where Anthropic's Claude Desktop rejected a newly added tool despite passing all server-side and independent validation tests. The problem stemmed from the tool's `outputSchema`, generated using `zodToJsonSchema`, which contained constructs like `$schema` pointing to draft-07 and specific type definitions that Anthropic's internal tool-ingest layer found unacceptable. This highlights the critical need for end-to-end testing, as validation layers can have stricter requirements than generic schema validators, leading to unexpected rejections. AI

IMPACT Highlights potential integration challenges for developers using AI models with strict tool-use validation layers.

RANK_REASON The cluster describes a specific issue encountered when integrating a tool with a product, highlighting a problem in the product's validation layer.

Read on dev.to — MCP tag →

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COVERAGE [1]

  1. dev.to — MCP tag TIER_1 English(EN) · Martin Havel ·

    Your MCP Server Passes Every Test — and Claude Still Rejects the Tool

    <p>We shipped what looked like a routine improvement to one of our MCP tools: a declared <code>outputSchema</code>, generated from our existing Zod types. Server-side smoke tests passed. The structured output validated cleanly against JSON Schema 2020-12 with an independent valid…