smt-sudoku-mcp: Instructions file for Codex

AGENTS.md

This file provides guidance to coding agents (Claude Code, Codex, and similar tools) when working with code in this repository.

Project

smt-sudoku-mcp: an MCP server demonstrating SMT/Z3 constraint solving via Sudoku. Four tools: generating a puzzle, validating a partial grid, validating a full solution, and solving a puzzle (or reporting why it cannot be solved).

Commands

uv manages the Python 3.13 environment — do not use pip directly. Commands run either via plain uv run or the justfile (just -l lists every recipe).

just install              # sync minimal (runtime-only) dependencies
just install-all          # sync all dependency groups (dev, test)
just format                # ruff format + ruff check --fix
just type-check             # uv run ty check
just test-coverage           # pytest (via coverage) across tests/, then coverage report
just launch-inspector        # run the MCP Inspector against the server (needs nvm/node)
just run-streamable-http      # run the server over streamable-http, for use with the Inspector
just vulnerability-scan       # osv-scanner over the source tree
just install-pre-commit-hooks / just pre-commit-update  # manage hooks via `prek`, not `pre-commit`

Run a single test:

uv run pytest tests/test_sudoku.py::TestSolvePuzzle::test_satisfiable -v

just test-coverage enforces fail_under = 100 (see [tool.coverage.report] in pyproject.toml); use # pragma: no cover for genuinely unreachable branches rather than writing tests around them. Running a single test with plain pytest/uv run pytest skips the coverage gate, which is expected during iterative development.

Ruff (line length 120, Google-style docstrings, isort, pyupgrade, complexity ≤ 15) and ty are also run by pre-commit hooks (.pre-commit-config.yaml), installed with prek, not the pre-commit CLI.

Architecture

Core logic (sudoku.py)

src/smt_sudoku_mcp/sudoku.py holds the SudokuGrid/Cell/result Pydantic models and all Z3 encoding, generation, validation, and solving logic. It has no FastMCP import at all, so it can be exercised directly in tests without going through the MCP protocol. Cell coordinates are 0-indexed internally (rows[r][c]), but any output field that names a specific cell (e.g. Cell) reports 1-indexed row/col, matching how Sudoku cells are conventionally described in text.