My MCP server config worked in Claude Desktop. It failed validation in OpenCode. Same protocol, different schemas.

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MCP config that works in Claude Desktop fails in OpenCode. Same protocol, different schema. A tale of subtle incompatibilities.

What Happened

OpenCode config validation failed with “Invalid input mcp.mcp-image” error. The MCP server configuration used wrong schema format.

The Broken Config

"mcp-image": {
  "type": "stdio",           // WRONG
  "command": "npx",          // WRONG
  "args": ["-y", "mcp-image"], // WRONG
  "env": {                   // WRONG field name
    "GEMINI_API_KEY": "...",
    "IMAGE_OUTPUT_DIR": "..."
  }
}

Investigation

1. First tried adding "type": "stdio" - still failed
2. Fetched official OpenCode docs at opencode.ai/docs/mcp-servers
3. Discovered correct schema from docs

Resolution

"mcp-image": {
  "type": "local",                           // local, not stdio
  "command": ["npx", "-y", "mcp-image"],    // array, not separate args
  "environment": {                           // environment, not env
    "GEMINI_API_KEY": "...",
    "IMAGE_OUTPUT_DIR": "..."
  }
}

Key differences:

• type: "local" not "stdio" (OpenCode terminology)
• command is a single array including args, no separate args field
• environment not env for env vars

Lesson

OpenCode MCP schema differs from Claude Desktop’s MCP schema. Always check vendor docs - don’t assume schema compatibility between different MCP hosts.