MCP Server

Kōdo ships with a built-in Model Context Protocol (MCP) server that exposes the compiler as a set of tools AI agents can invoke natively.

Quick Start

# Build the MCP server
cargo build -p kodo_mcp

# The binary is `kodo-mcp`
./target/debug/kodo-mcp

The server reads newline-delimited JSON-RPC 2.0 requests from stdin and writes responses to stdout, following the MCP stdio transport.

Configuration

Add kodo-mcp to your AI agent’s MCP configuration. For example, in Claude Desktop:

{
  "mcpServers": {
    "kodo": {
      "command": "/path/to/kodo-mcp"
    }
  }
}

Available Tools

The server exposes 6 tools:

kodo.check

Type-check Kōdo source code and return structured errors with fix patches and repair plans.

Parameters:

Name	Type	Required	Description
source	string	yes	Kōdo source code to check
filename	string	no	Optional filename for error reporting

Response (success):

{
  "status": "ok",
  "module": "example",
  "errors": [],
  "warnings": []
}

Response (errors):

{
  "status": "failed",
  "errors": [
    {
      "code": "E0200",
      "message": "type mismatch: expected `Int`, found `String`",
      "span": { "start": 42, "end": 48 },
      "suggestion": "change the value to match type `Int`",
      "fix_patch": {
        "description": "change type to `Int`",
        "start_offset": 42,
        "end_offset": 48,
        "replacement": "42"
      }
    }
  ]
}

kodo.build

Compile source through the full pipeline: parse → type-check → contracts → desugar → MIR. Native codegen is not available in the MCP context (source-only), but MIR success proves the program is well-formed through all compiler phases.

Parameters:

Name	Type	Required	Description
source	string	yes	Kōdo source code to compile

Response (success):

{
  "status": "ok",
  "module": "example",
  "phase": "mir",
  "message": "compilation successful (through MIR)",
  "function_count": 3
}

kodo.fix

Collect auto-fix patches and multi-step repair plans for all errors in the source. This is the core tool for the error → fix → recompile agent loop.

Parameters:

Name	Type	Required	Description
source	string	yes	Kōdo source code to fix

Response (errors found):

{
  "status": "errors_found",
  "error_count": 1,
  "patches": [
    {
      "error_code": "E0200",
      "description": "change type to `Int`",
      "start_offset": 74,
      "end_offset": 94,
      "replacement": "Int"
    }
  ],
  "repair_plans": [
    {
      "error_code": "E0200",
      "message": "type mismatch",
      "steps": [
        {
          "id": 0,
          "description": "wrap in Result::Ok",
          "patches": [{ "start_offset": 10, "end_offset": 15, "replacement": "Result::Ok(val)" }]
        }
      ]
    }
  ]
}

Response (no errors):

{
  "status": "ok",
  "message": "no errors to fix",
  "patches": [],
  "repair_plans": []
}

kodo.describe

Return module metadata: functions (with signatures, contracts, annotations), type declarations, and meta block.

Parameters:

Name	Type	Required	Description
source	string	yes	Kōdo source code to describe

kodo.explain

Explain a compiler error code with description, common causes, and fix suggestions.

Parameters:

Name	Type	Required	Description
code	string	yes	Error code (e.g. E0200)

kodo.confidence_report

Generate a confidence report for all functions in a module, based on @confidence and @reviewed_by annotations.

Parameters:

Name	Type	Required	Description
source	string	yes	Kōdo source code to analyze

Protocol Details

Supported Methods

Method	Description
initialize	Handshake — returns server info and capabilities
tools/list	Returns all 6 tool definitions with JSON Schema
tools/call	Invokes a tool by name with arguments

Error Codes

Standard JSON-RPC 2.0 error codes:

Code	Meaning
-32700	Parse error (malformed JSON)
-32601	Method not found / unknown tool
-32602	Invalid params (missing required parameter)

Example Session

# Initialize
echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{}}' | kodo-mcp

# List tools
echo '{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}' | kodo-mcp

# Check source
echo '{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"kodo.check","arguments":{"source":"module test {\n    meta { purpose: \"test\" }\n    fn main() -> Int {\n        return 42\n    }\n}\n"}}}' | kodo-mcp

Agent Integration Pattern

The recommended agent workflow with Kōdo MCP:

1. Write — agent generates .ko source
2. Check — call kodo.check to validate
3. Fix — if errors, call kodo.fix to get patches
4. Apply — apply patches to source (byte offsets)
5. Build — call kodo.build to verify full pipeline
6. Repeat until status: "ok"

For complex errors, repair_plans provide multi-step sequences. Each step has an id and patches should be applied in order.