AgentArmorHQ
Sign in
  • AgentArmor teamTeam2d agoNeeds helpSolved

    Cline 3.16.3 MCP config fails validation — transportType workaround

    After updating Cline to 3.16.3 on Windows 11, my MCP server configuration started failing validation. A standard config like { "mcpServers": { "memory": { "url": "http://ip:8030/sse/memory", "type": "sse" } } } is rejected, and the error message doesn't show the expected structure. What changed in 3.16.3 and how can I get my MCP servers working again?

    Originally asked on GitHub: https://github.com/cline/cline/issues/3705

    6 answers

    • Best answerAgentArmor teamTeam2d ago

      This issue is closed as completed; a maintainer said a quick fix was in progress, though the thread doesn't state the exact release that fixed it. The break was in Cline 3.16.3. A contributor suspected commit 8356e058c1c2efcb0c8ec13bec624bed55b1f155, which switched MCP server validation to a z.discriminatedUnion("transportType", ...) schema covering stdio, SSE, and streamable-http configs — so every MCP server entry now needs a transportType property, and the validation error doesn't tell you that.

      The confirmed workaround: add "transportType": "stdio" to each command-based server entry:

      json
      {
  "mcpServers": {
    "server1": {
      "transportType": "stdio",
      "command": "python",
      "args": ["/path/to/server.py"],
      "env": { "API_KEY": "your_api_key" },
      "alwaysAllow": ["tool1", "tool2"],
      "disabled": false
    }
  }
}

      Only "stdio" was confirmed working in the thread — nobody tested a transportType value for SSE or streamable-http servers, so if you use those transports, expect to experiment. Reverting to 3.16.2 restored MCP for one user, but another user reported the revert didn't help. The maintainer who acknowledged the regression later folded the issue into the broader MCP tracking issue #4391. General advice: MCP configs frequently contain API keys in env, so keep them out of version control.

      Did this work for you?
    • AgentArmor teamTeam2d ago

      What @stevenaldinger tried on GitHub (Worked)

      Added "transportType": "stdio" to the MCP server config so it matched the new discriminated-union schema; MCP servers updated properly afterwards.

      Source: https://github.com/cline/cline/issues/3705#issuecomment-2899699957 (opens external site)

      Did this work for you?
    • AgentArmor teamTeam2d ago

      What @stampcli tried on GitHub (Worked)

      Reverted Cline from 3.16.3 back to 3.16.2 to get MCP servers working again.

      Source: https://github.com/cline/cline/issues/3705#issuecomment-2899483060 (opens external site)

      Did this work for you?
    • AgentArmor teamTeam2d ago

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

      Also reverted to 3.16.2 after the update broke the MCP setup, but the configuration remained broken and couldn't recover.

      Source: https://github.com/cline/cline/issues/3705#issuecomment-2899610638 (opens external site)

      Did this work for you?
    • AgentArmor teamTeam2d ago

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

      Reproduced the failure on macOS arm using the official Cline docs' local stdio MCP example (command, args, env, alwaysAllow, disabled).

      Source: https://github.com/cline/cline/issues/3705#issuecomment-2899498518 (opens external site)

      Did this work for you?
    • AgentArmor teamTeam2d ago

      What @vk2r tried on GitHub (Didn't work)

      Reported the failure on Cline 3.16.3 / Windows 11 with an SSE memory server config: { "mcpServers": { "memory": { "url": "http://ip:8030/sse/memory", "type": "sse" } } }; the validation error didn't show the expected structure.

      Source: https://github.com/cline/cline/issues/3705 (opens external site)

      Did this work for you?

    Add your answer or comment