Mason

Mason

Preserve why your code was built this way.

Record the reason · Review the lesson · Surface applicable guidance · Reconsider it as code changes

Mason preserves reviewed engineering reasoning with your repository, so future maintainers and coding agents can retrieve the evidence behind consequential decisions. Record workarounds, rejected approaches and constraints while their reasons are available; revisit them when the underlying code changes.

Get started

Install on macOS or Linux:

curl -fsSL https://github.com/adrianczuczka/mason/releases/latest/download/install.sh | sh

Windows PowerShell:

irm https://github.com/adrianczuczka/mason/releases/latest/download/install.ps1 | iex

No Node or npm required. Git is required. The installer configures PATH for Bash, Zsh, and Windows. Platform details · npm installation

New standard standalone installs update automatically in the background. Updates activate on a future MCP launch after existing Mason MCP servers exit. Run mason updates to inspect or change this preference. Existing installations require one manual upgrade and mason updates enable. Update controls

Run this in your Git repository (open a new terminal if the installer asks):

mason init --host codex    # Maintainer: prepare shared configuration for review/commit

mason setup --host codex # Each developer: activate locally

For Claude Code, use --host claude.

If the repository already has compatible Mason configuration, run only mason setup. Initialization prepares MCP, hooks and project instructions; setup leaves shared files untouched. Review your host's trust settings, start a new session, and give your agent a normal task.

Check that Mason is being used:

mason status

Setup uses your installed mason command—no project launch scripts or runtime copies. Status distinguishes configuration from observed use. Setup and upgrades · Disconnect a project · Other MCP clients

Try a check without setup

mason audit --dir .

mason review --dir . --base origin/main

The audit checks claims in README and agent instruction files throughout the repository. The review checks committed changes against your chosen base. Both are read-only and need no model calls.

What Mason catches

After resolving an incident or settling a constraint, ask your agent to record a sourced proposal with Mason. Review it before accepting it as project guidance. Later tasks can retrieve the operative accepted revision while proposed replacements remain distinct, and changes to referenced code can prompt inspection, revision or retirement.

Mason complements tests, linters, and code review. Findings are evidence to inspect; unavailable checks stay explicit.

Evidence so far

Earlier read-only decision-retrieval evaluations scored 9.0/10 with Mason vs 7.0/10 without. The initial ten-task patch comparison tied at 10/10 for both. Improved patch outcomes remain to be demonstrated. Results, methodology, and limitations

Maintained notes also succeeded in the reuse trials. Recent hook experiments verified supported file delivery, with additional context cost and no demonstrated correctness gain; direct delivery for ordinary Bash workflows remains open. The current focus is useful preservation and reuse of engineering reasoning during ordinary work, with capture and maintenance effort that feels worthwhile. Preventing repeat mistakes is one intended benefit; comparative superiority remains unestablished. Positioning and validation plan · Current evidence

Documentation

• Setup, hooks, and upgrades
• Data and network behavior · Hook performance
• Audits, repair verification, and CI evidence
• Decisions, tools, and optional architecture maps
• Roadmap · Changelog · MIT license

Development

For development, use Node 20 (20.19+), Node 22 (22.13+), or Node 24+. After npm ci, run npm run format to format TypeScript sources, tests, and tooling configs. CI checks formatting with npm run format:check and runs npm run lint, npm run typecheck, and the test suite. Run npm test locally to check behavior.

ESLint uses the recommended TypeScript rules plus type-aware checks for unhandled promises, misused async callbacks, and invalid awaits. Prettier handles formatting. Test fixtures and generated outputs are excluded from formatting and linting. Production sources also reject explicit any and unsafe assignments, property access, calls, arguments, and returns. External data is validated before use. Test doubles keep the more permissive rules.