Sounio MCP Server

sounio-mcp-server exposes the checked Sounio compiler to agentic tools over local Model Context Protocol stdio transport. It is intentionally local-only: no HTTP transport, no OAuth, no token handling, and no remote execution path.

Install

pip install -e tools/mcp
python -m sounio_mcp.server --transport stdio

Claude Code:

claude --mcp-server sounio=python:-m:sounio_mcp.server

The server resolves souc through scripts/lib/resolve_souc.sh, which in this checkout resolves to the checked self-hosted launcher (bin/souc on supported hosts). The server rejects source paths outside /workspace/sounio.

Tool calls return both MCP text content and structuredContent. The text content keeps the prompt's shell examples simple; structuredContent lets typed MCP clients consume the result without reparsing JSON text.

Tools

sounio_check

Type-checks a .sio file and returns diagnostics normalised from souc check --json.

Example:

{
  "source_path": "tests/fixtures/broken_dose.sio"
}

The response includes two diagnostic views:

• diagnostics: agent-friendly records with string severity, one-based line/column, spans, related notes, and warnings.
• diagnostic_envelope: the CC-1/CC-2 shared sounio.diagnostic.v1 envelope validated against tools/shared/diagnostic_schema.json.

sounio_compile

Runs sounio_check, then compiles a valid file to a local artefact.

Example:

{
  "source_path": "examples/hello.sio",
  "target": "elf",
  "optimization": "default"
}

Targets are accepted as elf, macho, ptx, metal, or wasm. The current checked launcher is strongest for host-native ELF; other targets are passed through to the compiler target flag and reported honestly if unsupported.

sounio_run

Runs souc run, captures stdout/stderr/exit code, and reports compile_error, runtime_error, timeout, or ok.

Example:

{
  "source_path": "examples/hello.sio",
  "args": [],
  "timeout_sec": 30
}

Environment overrides are allowed only for non-sensitive keys. Keys containing tokens, secrets, credentials, proxies, or auth material are rejected.

sounio_test

Runs a Sounio test directory or file programmatically using the checked compiler.

Example:

{
  "test_pattern": "tests/run-pass",
  "test_filter": "hello"
}

The test runner understands the existing //@ run-pass, //@ compile-fail, //@ check-only, //@ expect-stdout, //@ expect-stdout-contains, //@ error-pattern, and //@ ignore annotations.

Resources

• sounio://stdlib/{module} returns stdlib README/source context.
• sounio://errors/{error_code} returns compiler error explanations traced to current compiler source or committed compile-failure evidence.

Examples:

sounio://stdlib/stats
sounio://stdlib/clinical
sounio://errors/E070

Error -> Fix Loop

The loop is deliberately thin:

1. Agent writes or edits a .sio file.
2. Agent calls sounio_check.
3. Diagnostics are injected into the next prompt.
4. Agent revises the file.
5. Agent repeats until diagnostics are empty or the iteration budget is reached.

The reproducible local demonstration is:

PYTHONPATH=tools/mcp python3 tools/mcp/examples/llmloop_recipe.py \
  --fixtures 'tests/fixtures/broken/*.sio' \
  --max-iter 10 \
  --seed 1729

Current fixture benchmark:

• fixtures: 20
• agent model: deterministic-fixture-agent-v0.1
• seed: 1729
• convergence rate: 1.0
• average iterations: 1.0

This is a local recipe for the LLMloop pattern, not a claim about a hosted model. It exists so Claude Code, Cursor, ChatGPT via MCP, and CLI agents can close the same check/fix/re-check loop using the real Sounio compiler.

Cross-Agent Use

• CC-1 owns tools/shared/diagnostic_schema.json; MCP consumes the same souc check --json shape and keeps the LSP-compatible range fields.
• Cx-1 should use sounio_check as the canonical validation method for generated dataset examples.
• Cx-2 can use sounio_run as the HumanEval/MultiPL-E execution harness once translated .sio files are produced.

Quality Notes

• No compiler binary is modified.
• No remote MCP transport is implemented.
• Error catalogue entries are trace-backed; unknown codes return an explicit "not promoted yet" resource instead of invented explanations.
• The checked launcher's compile compatibility mode may exit zero even when an artefact is not emitted, so sounio_compile verifies output existence.
• The focused Python gate covers direct tools, schema validation, one-shot JSON-RPC, and an actual mcp Python SDK client session over stdio.