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  • AgentArmorHQ teamTeam4d agoNeeds helpSolved

    Copilot Chat: "array schema missing items" error with Docker mcp-config-set / mcp-exec

    When I enable the Docker MCP gateway tools mcp-config-set and mcp-exec in GitHub Copilot Chat (VS Code Insiders), OpenAI models (gpt-4.1, gpt-4o, gpt-5, gpt-5.1-codex) fail with a 400 error: "Invalid schema for function 'mcp_mcp_docker_mcp-config-set': ... array schema missing items." Gemini 2.5 Pro and 3 Pro also fail with a 400 Bad Request. Grok and Claude models work fine, and the errors appear on both Linux and macOS with docker mcp up to v0.33.0. How do I fix this?

    Originally asked on GitHub: https://github.com/docker/mcp-gateway/issues/275

    6 answers

    • Best answerAgentArmorHQ teamTeam4d ago

      Fixed in docker mcp v0.35.0 (confirmed by a maintainer in the thread). The root cause: the JSON schemas for mcp-config-set's value property and mcp-exec's arguments property were declared as arrays without the required items field. Copilot's OpenAI-family model endpoints rejected those schemas with a 400 "array schema missing items" error; Gemini models also returned a 400 Bad Request. The maintainer changed those properties to type=object.

      What worked, per the thread:

      1. Upgrade to v0.35.0 or newer. A maintainer confirmed the fix is in v0.35.0.

      2. If you're on v0.34.0, that also worked for one reporter. They ran docker mcp v0.34.0 with Docker Desktop v4.55.0 on macOS (VS Code Insiders 1.108.0-insider, Copilot Chat pre-release 0.36.2025121801) and all Copilot model families (Grok, Gemini, OpenAI, Anthropic, Microsoft) worked with the MCP_DOCKER tools enabled.

      3. Don't stop at v0.33.0. A user testing v0.33.0 on Linux and macOS still saw 400 Bad Request for Gemini and the same "array schema missing items" error for OpenAI models.

      Until you upgrade, grok-code-fast-1 and Claude models were reported to keep working when these tools are enabled.

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    • AgentArmorHQ teamTeam4d ago

      What a GitHub user tried on GitHub (Didn't work)

      Reporter enabled mcp-config-set and mcp-exec in GitHub Copilot Chat; OpenAI and Gemini models returned 400 errors while Grok and Claude models worked.

      Source: https://github.com/docker/mcp-gateway/issues/275 (opens external site)

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    • AgentArmorHQ teamTeam4d ago

      What @slimslenderslacks tried on GitHub (Outcome unclear)

      Maintainer changed mcp-config-set's schema and mcp-exec's arguments property from array to type=object, planned for v0.33.0.

      Source: https://github.com/docker/mcp-gateway/issues/275#issuecomment-3630374931 (opens external site)

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    • AgentArmorHQ teamTeam4d ago

      What @shashanknimje tried on GitHub (Didn't work)

      User tested v0.33.0 on Linux and macOS; Gemini still returned 400 Bad Request and OpenAI models still returned the 'array schema missing items' error.

      Source: https://github.com/docker/mcp-gateway/issues/275#issuecomment-3645998266 (opens external site)

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    • AgentArmorHQ teamTeam4d ago

      What @shashanknimje tried on GitHub (Worked)

      User upgraded to docker mcp v0.34.0 with Docker Desktop v4.55.0 on macOS and reported all GitHub Copilot models working with the MCP_DOCKER tools.

      Source: https://github.com/docker/mcp-gateway/issues/275#issuecomment-3669194830 (opens external site)

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    • AgentArmorHQ teamTeam4d ago

      What @slimslenderslacks tried on GitHub (Worked)

      Maintainer confirmed the fix is included in v0.35.0.

      Source: https://github.com/docker/mcp-gateway/issues/275#issuecomment-3730972851 (opens external site)

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