Bouncer Gates

bouncer-gates

Five checks that stop the expensive mistakes before they merge, whether a person or an agent wrote the code.

Hardcoded secrets. Database queries that leak one customer's data to another. Float maths on money. Migrations that break the running app. Docs that link to files which no longer exist.

Agents write most new code now, and they make exactly these mistakes: a key pasted in to make a test pass, a query with no tenant filter because the prompt never mentioned tenants. bouncer-gates runs inside Claude Code and Cursor, so the agent hears about it in the same turn it wrote it, and again in CI so nothing gets through.

Try it on any repository in ten seconds:

npx bouncer-gates

Or paste some code into the playground and watch the same checks run on it.

Quick start

npx bouncer-gates --init          # writes bouncer-gates.config.json, reads your Prisma schema if you have one
npx bouncer-gates --init-agents   # wires the same checks into Claude Code and Cursor for this repo
npx bouncer-gates                 # runs every check and prints what it found

Add it to GitHub Actions:

steps:
  - uses: actions/checkout@v4
    with:
      fetch-depth: 0             # needed so the migration check can see what is new
  - uses: ajeermahmood/bouncer-gates@v0
    with:
      version: "0.5.0"

That is the whole setup. Everything below is detail.

In the editor, with the agent

--init-agents commits two things into the repository: an MCP server the agent can call, and a hook that scans every file the agent writes. When a file has a blocking finding, the agent sees the file, the line, what is wrong and what to do instead, in the same turn:

x src/orders.ts:12  scope/unscoped-query
  "order" is tenant-owned, but nothing in this query mentions "tenantId", so it returns rows from every tenant.
  fix: Add tenantId to the where clause, or go through a tenant-scoped client.

Any other MCP client can run npx -y bouncer-gates --mcp, and any post-edit hook can pipe its event to npx -y bouncer-gates --hook. How it works, and what it will not do.

What it checks

Each check exists because of a real, expensive bug. None is a style opinion. The gate reference explains every rule with a bad example and a fixed one.

When it finds something

Every finding names the file, the line, what is wrong and what to do instead:

  FAIL  scope

    x src/orders.ts:2  scope/unscoped-query
      "order" is tenant-owned, but nothing in this query mentions "tenantId", so it returns rows from every tenant.
      fix: Add tenantId to the where clause, or go through a tenant-scoped client.

You have three options, in this order:

1. Fix it. Usually the right answer.
2. Explain why it is fine. Put a comment on the line, or the line above it, with a reason. The reason is required; a bare marker does nothing.

   // bouncer-gates-ok(scope): nightly revenue report spans every tenant by design
   const all = await prisma.order.findMany();
   

3. Record existing problems so only new ones block. On a codebase that already has findings, run this once and commit the file it writes:

   npx bouncer-gates --baseline-write
   

   Old findings stop blocking. Anything new still does. The file is readable, and the count in it should only ever go down.

Configuration

bouncer-gates --init writes this for you. Edit it by hand any time.

{
  "exclude": ["fixtures/**"],
  "scope": {
    "models": ["order", "customer"],
    "tables": ["orders", "customers"],
    "column": "tenantId",
    "clients": ["prisma"],
    "rawAccessor": "raw"
  },
  "doc-links": { "repoUrl": "https://github.com/you/your-repo" }
}

• exclude: files not to scan at all. The run prints how many files each pattern removed, every time, so the list cannot grow quietly.
• scope.models / tables: the models and tables that belong to a tenant. --init fills these from any model in your Prisma schema that has a tenantId field.
• scope.clients: plain client names, like prisma, whose queries should be checked for the tenant column. Use this when you do not have a scoped wrapper.
• scope.rawAccessor: if you do have a scoped wrapper, this is the name of the raw client it hides, like db.raw. Reaching for it gets flagged.
• doc-links.repoUrl: lets absolute links back to your own repository be checked as file paths too.

Without a scope section, the scope check reports skipped, not passed.

All the commands

npx bouncer-gates                        # every check, whole repository
npx bouncer-gates --init                 # write a starter config
npx bouncer-gates --init-agents          # wire the gates into Claude Code and Cursor
npx bouncer-gates --mcp                  # serve the gates over MCP, for any agentic editor
npx bouncer-gates --hook                 # scan the file named by a hook event on stdin
npx bouncer-gates --changed              # only files this branch touched
npx bouncer-gates --only scope,money     # just some checks
npx bouncer-gates --explain scope        # what a check does and how to excuse a case
npx bouncer-gates --baseline-write       # record existing findings
npx bouncer-gates --json                 # machine-readable output
npx bouncer-gates --sarif                # for the GitHub Security tab

Exit code 0 means clean, 1 means something blocked, 2 means the tool itself could not run (bad flag, broken config, not a git repository). CI treats 1 and 2 differently on purpose: a broken tool should not look like a codebase full of problems.

What it does not do

Honest limits, so nobody trusts it further than it deserves:

• It matches shapes in text. It does not understand your code. A tenant filter built in a helper the check cannot see will be reported, and the comment above is the fix.
• The money and scope checks only read JavaScript and TypeScript.
• The migration check only reads .sql files. Migrations written in JavaScript or TypeScript are not checked.
• Secrets split across lines, or with no recognisable prefix, are not found. For deep history scanning use gitleaks or trufflehog; this is the cheap guard on the door, not the audit.
• A query inside prisma.$transaction(async (tx) => ...) uses a client the check cannot follow.

Every rule's blind spots are listed in the gate reference.

Words used here

• Gate or check: one of the five things it looks for.
• Finding: one problem it reports, with a file and line.
• Blocking: a finding that makes the run exit 1. Warnings do not.
• Baseline: the file that records findings you have chosen to live with for now, so only new ones block.
• Acknowledge or excuse: the bouncer-gates-ok comment that says a specific line is fine, and why.

Telemetry

One anonymous ping a day: a random id, the version, the runtime, the OS and the Node major. Nothing about your code, ever. BOUNCER_TELEMETRY=0 turns it off. Everything it sends.

More

• Inside the editor: the MCP server and the hook, what the agent sees, other editors
• Gate reference: every rule, a bad and a good example, what it misses
• Rolling it out on an existing codebase
• Design notes: why it never fails open, why findings never quote the secret, the false-positive story, and the speed work
• Architecture: gates are pure functions, which is why the same code runs in the CLI, in a Cloudflare Worker and in your browser
• Deployment: the playground, the API and npm
• Contributing: adding a gate, and how to decide whether something should be one

Development

npm install
npm test                        # unit tests
npm run check                   # bouncer-gates on itself
npm run bench -- ../some-repo   # measure against a real codebase
npm run dev                     # the playground site

Licence

MIT. Take any of it.

Built by Ajeer Mohammed. The rules come from the checks that gate a multi-tenant platform where most of the code is written by a coding agent, and where missing one meant a merchant seeing another merchant's orders. How that workflow fits together.