open source · deterministic guardrails

Rules that run, not notes that get ignored

becwright enforces constraints on your code deterministically. Instead of asking an AI agent to respect a rule — the way CLAUDE.md or .cursorrules do — it verifies the result and blocks the commit when the rule is broken.

Get started → View on GitHub

npm · pnpm · pipx — a self-contained binary, no Python required

pre-commit · becwright

$ git commit -m "feat: session logging"

▸ becwright check

✓ no-dangerous-eval pass

✓ no-debug-remnants pass

✗ no-token-in-logs BLOCKED

src/auth/session.py:42 — token leaked into a log

commit aborted — 1 blocking rule failed

The problem

A note is a promise. A commit ships anyway.

An AI agent writes code and leaves a note: “this must never log session tokens.” That note is text. Three months later another agent regenerates the module, never reads it, and drops the token into the logs. Nobody notices until it blows up in production.

Notes are probabilistic — they depend on the agent reading, understanding and obeying. becwright is deterministic: the rule runs against the real code and returns pass/fail, no matter which agent or model made the change.

// The two layers are complementary: CLAUDE.md prevents, so 95% comes out right the first time. becwright is the safety net for the 5% that slips through.

diff · note vs rule

	− Note in CLAUDE.md	+ becwright rule
What it does	Asks to be respected	Verifies it was respected
Depends on	The agent reading and obeying	Nothing — it runs against the code
Result	Likely	Guaranteed
Analogy	A “speed limit” sign	A physical bump in the road

Core concept

A BEC is a Bound Executable Constraint

Three properties that no current artifact has together. Each one closes a gap the others leave open.

B intent · why_it_matters

Bound

The rule is born tied to the intent and the decision that created it — the why. It is not a loose rule without context.

E check → exit 0 | 1

Executable

It carries a check that runs and returns pass/fail (exit code 0 or 1). It is not prose someone promises to respect.

P export → import

Portable

It can be exported from one repo and imported into another, like a package. This is what creates the network effect over time.

How it works

Installed once. It runs on every commit.

01

Install the engine

Pick your ecosystem. The npm packages ship a self-contained binary — no Python needed.
02

Scaffold your rules

becwright init detects your language, writes .bec/rules.yaml and installs the native git hook.
03

Commit — it checks

Every commit runs the checks over staged files. If a blocking rule fails, the commit stops.

.bec/rules.yaml

rules:
  - id: no-token-in-logs
    intent: >
      Session tokens and credentials must
      never reach any log.
    why_it_matters: >
      If a token shows up in the logs,
      anyone with access can steal a session.
    paths: ["src/**/*.py"]
    check: "becwright run no_token_in_logs"
    severity: blocking   # stops the commit

Included checks

Ready-to-use checks, each tied to its why

Text/regex based and conservative by design. The value is binding each rule to the reason it exists — and you can write your own in any language.

check Detects Lang Severity

forbid Any regex you pass (--pattern) any depends
no_token_in_logs Tokens / credentials in log calls Python blocking
hardcoded_secrets AWS keys, private keys, password = "…" literals any blocking
debug_remnants Forgotten breakpoint(), pdb.set_trace(), import pdb Python blocking
dangerous_eval eval() / exec() calls any blocking
wildcard_imports from x import * Python warning

Any language

The engine only filters files by their paths globs and runs the check as a command — it never assumes Python. Watch JavaScript, Go, Rust, or anything else with the generic forbid check or your own script.

Built for AI agents

The deterministic net for what an agent lets slip

CLAUDE.md asks an agent to behave. becwright is the guard that checks — and the agent can install and drive it for you. The Claude Code plugin gives any session a becwright skill and a /becwright command; results are exposed as structured data to any MCP agent.

▸ becwright skill

Auto-invoked when you ask for a guardrail. The agent knows how to install, scaffold rules, and read and fix check output.
▸ /becwright command

One entry point: init · check · add · status — install, run, and import BECs without leaving the chat.
▸ check --json

Machine-readable pass/fail with intent and why — no parsing, works from the standalone binary.
▸ MCP server

Exposes check and list_checks as tools to any MCP agent — Claude, Cursor, Windsurf.

Claude Code plugin

/plugin install becwright@becwright

/becwright init

▸ becwright check --all

✓ no-dangerous-eval pass

✗ no-token-in-logs BLOCKED

src/auth.py:42 — fixing…

✓ commit unblocked

Get started

Three commands to a guarded repo

npm pnpm pipx

# 1. Install the engine

$ npm install --save-dev becwright

# 2. Scaffold rules + install the hook

$ becwright init

✓# 3. Done — every commit runs the checks

npm packages cover linux-x64, linux-arm64, darwin-x64, darwin-arm64 and win32-x64. On any other platform use pipx install becwright.

Contribute

Found a bug? Have an idea?

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Prefer GitHub’s templates? Bug report Feature request BEC proposal · Browse existing issues →

Backed by teams who believe in deterministic guardrails

becwright is open source and grows with the support of the people and companies who use it.

Stop trusting notes. Start enforcing rules.

becwright is open source and the installable MVP is verified end-to-end. Bring deterministic guardrails to your repo today.

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