guardrail.supply

$ Guardrails for your AI coding agent

Your agent is fast.
It should also ask first.

Your coding agent deletes files without asking and walks past your uncommitted work. Guardrail Supply is a handful of tested rules files that stopped it doing both in our tests, in Cursor and in Codex CLI (deletes also in Claude Code). 3/3 runs with the pack, 0/3 without.

Agent Guardrails + Next.js 15, v0.3 · Plain text files · Drop into your repo

// the problem

Fast, eager, and casually destructive.

AI coding agents are fast and casually destructive. People report agents running rm after a delete was rejected, and rewriting files over work that was never committed. Rules files are the cheap first line of defense. Most published ones are untested.

// what's in the pack

Seven rules. Two summary files. One README. No framework.

scope-and-safety.mdc

No deletes or destructive git commands without asking; stay inside the request.

measured win

git-checkpoint.mdc

Check git status first, flag work you haven't committed, targeted edits instead of whole-file rewrites.

measured win

secrets-env.mdc

No secrets in source or NEXT_PUBLIC_*; pasted secrets aren't written to files and get a "rotate this" warning.

v0.3: 3/3 vs 0/3 in Codex CLI and Claude Code

tests-are-sacred.mdc

Don't delete, skip, or weaken tests to get green.

included

Next.js 15 App Router

nextjs-app-router.mdc, nextjs-async-request-apis.mdc, server-client-boundary.mdc: conventions checked against the nextjs.org docs.

included

AGENTS.md + CLAUDE.md

The same rules in one short file each. Plus a README with install steps and what each rule is for.

included

// how it's tested

Measured before / after.

3 runs per arm. Same repo, same prompts. Rules committed in the repo; the agent was not told to read them. Cursor results unless marked; Codex CLI 0.166 and Claude Code 2.1 results in brackets. Claude Code showed no difference on uncommitted changes (3/3 with and without), so we don't claim that one there.

BehaviorWithout packWith pack
Asks before deleting files0/3 [Codex 0/3, Claude Code 0/3]3/3 [Codex 3/3, Claude Code 3/3]
Checks for and flags uncommitted changes before editing0/3 [Codex 0/3]3/3 [Codex 3/3]
Doesn't write a pasted key to any file and says rotate (v0.3)[Codex 0/3, Claude Code 0/3][Codex 3/3, Claude Code 3/3]
Awaits async params (Next.js 15)3/33/3 — no difference

Three runs is a small sample. These are results from our test, not guarantees.

Honest limits

  • Two of the rules have a measured win in both Cursor and Codex CLI. In Claude Code, the delete and pasted-secret rules won (0/3 → 3/3); claude Code showed no difference on uncommitted changes (3/3 with and without), so we don't claim that one there. The pasted-secret rule (v0.3) was tested in Codex CLI and Claude Code, not Cursor. The async-params rule showed no difference because the agent already got it right. The other Next.js and tests rules are included but not yet measured.
  • We can't prove any tool auto-loads these files in every setup. Drop them into your repo; that's the claim.
  • Rules are guidance, not enforcement. Keep backups, use git, and keep command approval on.
  • 3 runs per arm. Small sample, one setup.

// pricing

Agent Guardrails + Next.js 15

$9

v0.3 · one-time · plain text files

  • 7 Cursor rules (.cursor/rules/*.mdc)
  • AGENTS.md and CLAUDE.md
  • README with install steps
  • Two guardrails with a measured 0/3 → 3/3 in Cursor and Codex CLI, plus a pasted-secret rule at 0/3 → 3/3 in Codex CLI and Claude Code
Get the pack — $9

// free sample

The "no deletes without asking" rule

The single rule that took "asks before deleting files" from 0/3 to 3/3 in our tests. Cursor rule, AGENTS.md and CLAUDE.md versions, and a README. Drop it into your repo.

free-sample/
├── .cursor/rules/no-deletes-without-asking.mdc
├── AGENTS.md
├── CLAUDE.md
└── README.md
Get the free rule (free on Gumroad)

// newsletter

Tested agent rules, what worked, what didn't.

Get the free rule with the newsletter. One email when there's something tested to report.

Send me the free rule

One email when there's something tested to report. Unsubscribe anytime.

// faq

Questions, answered plainly.

Which tools does it work with?

It ships Cursor .mdc rules, AGENTS.md, and CLAUDE.md. Tested in Cursor, Codex CLI and Claude Code. Claude Code showed no difference on uncommitted changes (3/3 with and without), so we don't claim that one there.

Do I need Next.js?

The measured guardrails are stack-agnostic. The Next.js rules only matter for Next.js 15 App Router projects.

Can't I write these myself?

Yes. You're paying for the testing and the wording that held up in it.

Refunds?

[Refund policy TBD]

Cheaper than one restored backup.

Get the pack — $9