Borrowing it
Nothing to install: this file belongs to mmartinez/postern. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/mmartinez/postern/main/CLAUDE.mdgit clone --depth 1 https://github.com/mmartinez/posternWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/instructions/mmartinez/postern/claude-md)<a href="https://agentmods.dev/instructions/mmartinez/postern/claude-md"><img src="https://agentmods.dev/badge/instructions/mmartinez/postern/claude-md/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/instructions/mmartinez/postern/claude-md"><img src="https://agentmods.dev/badge/instructions/mmartinez/postern/claude-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.02726 | $0.02726 |
| Opus 5.5 | $0.01090 | $0.01090 |
| Sonnet 5.5 | $0.00545 | $0.00545 |
| Haiku 4.5 | $0.00273 | $0.00273 |
Grade A, and why
postern CLAUDE.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 17d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 151 lines — stays where its author put it; the contents beside it link to each section on GitHub.
What postern is
A credential-brokering HTTPS forward proxy for AI agents. The agent calls outbound APIs without auth headers (or with placeholder values); postern matches the request host against YAML-declared broker rules, resolves the rule's credential reference from a pluggable credential provider (1Password Service Accounts, Bitwarden Secrets Manager, OAuth2 token minting), and injects it before forwarding. The agent never holds the real credential.
Apache-2.0 licensed.
Development environment — container-first, non-negotiable
The host needs only Docker, git, and the devcontainer CLI. No Go toolchain on the host. Every Go, lint, test, format, and vuln tool lives inside the devcontainer, version-pinned by .mise.toml.
- Start the env once:
devcontainer up --workspace-folder . - Drop into a shell:
make shell - Anything Go-related goes through
make <target>. From the host these wrapdevcontainer exec; inside the container they are direct invocations. The Makefile auto-detects which side it's on. - Bump tool versions in
.mise.toml; the devcontainer reads these pins. CI pins Go/lint/goreleaser/zig separately in each workflow's env — bump both sides when a tool changes. - After bumping the Go pin, re-run
bash .devcontainer/post-create.shinside the container (make shell, then the script).govulncheckandgo-licensesarego installed into the active Go'sGOBIN, and their mise shims keep pointing at the previous toolchain until they are reinstalled — otherwisemake cistops at the vuln step withmise ERROR No version is set for shim: govulncheck.
If a command fails on the host with "command not found", the fix is to run it via make (or inside make shell), not to install the tool globally.
Commands
All Go work runs through make; on the host these wrap devcontainer exec.
make shell— interactive shell inside the devcontainer.make build— builddist/postern.make test— full suite with-raceand coverage.make lint— golangci-lint.make ci— lint + test + vuln + license check (the core local gate; CI adds platform, format, gitleaks, and snapshot/image jobs on top); run before pushing.make snapshot— local release build (binaries, archives, SBOMs, checksums; no publish/sign).make licenses— regenerateTHIRD_PARTY_NOTICES.mdafter any dependency change.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 17d ago Changed · +1 lines · +99 tokens per session 89d46e6396a1
- 24d ago Changed · +1 lines · +65 tokens per session d15d69123672
- 25d ago Changed · +1 lines · +102 tokens per session a6e193195226
- 1mo ago First seen · 148 lines · 2,460 tokens per session scan A cea31e3230ac
postern CLAUDE.md is an instructions file published in the GitHub repository mmartinez/postern (11 stars, last pushed 12d ago), licensed Apache-2.0. It adds 2,726 tokens to every session, about $0.0109 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
Other instructions, from other repositories
vscode buildNext.instructions.md
Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).
next.js AGENTS.md
AGENTS.md instructions for vercel/next.js, covering next.js development guide, codebase structure, monorepo overview, core package: packages/next and other important packages.
vscode oss-third-party-notices.instructions.md
Instructions for microsoft/vscode, covering vs code oss third-party-notices pipeline, architecture, pipeline flow in ci, cache eligibility and rollout and applying the notice (cutover).
langchain AGENTS.md
AGENTS.md instructions for langchain-ai/langchain, covering global development guidelines for the langchain monorepo, corridor security analysis, project architecture and context, monorepo structure and development tools & commands.
vscode copilot-instructions.md
Copilot instructions for microsoft/vscode, covering vs code copilot instructions, project overview, root folders, core architecture (src/ folder) and built-in extensions (extensions/ folder).
vscode model-prompts.instructions.md
Model-specific prompt authoring and registry guidelines.