Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add instructions/vercel-labs/fx/agents-mdgit clone --depth 1 https://github.com/vercel-labs/fxWhat 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 | $0.05949 | $0.05949 |
| Opus 5 | $0.02975 | $0.02975 |
| Sonnet 5 | $0.01190 | $0.01190 |
| Haiku 4.5 | $0.00595 | $0.00595 |
Grade A, and why
fx AGENTS.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 today.
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 — 469 lines — stays where its author put it; the contents beside it link to each section on GitHub.
AGENTS.md
Instructions for AI coding agents working with this codebase.
Declaring Work Ready
Do not say the work is "ready", "done", "good to go", "complete", or similar until you have personally run the binary and exercised the change on its happy path. A passing test suite is necessary, not sufficient — tests in this repo do not always construct the full runtime, attach a TTY, or spawn background threads, so they will not catch startup crashes, render regressions, or thread-lifetime bugs.
Before reporting the work as ready:
- Build succeeds.
- Focused tests for the changed path pass locally.
- The Full CI run for the exact current commit passes on every required Linux and macOS runner.
- Run the built binary locally and drive at least one real interaction that exercises the change end to end.
- Confirm the process did not abort, stderr is clean, and the behavior matches what you are about to tell the user.
If you cannot run the binary in your environment, say so explicitly and ask the user to verify. Do not silently skip this step and declare the work ready. "The tests pass" is not a substitute for running the app.
Always use the built binary in this repo
When running fx for verification, always use the freshly-built binary at ./zig-out/bin/fx from this checkout. Never run fx from PATH, never rely on whatever is at ~/.fx/bin/fx, and never assume an installed copy reflects your change.
-
The user may have an older
fxon their PATH (e.g. installed viafx upgradeor the CDN install script). Running that one will not exercise your edits. -
zig buildwrites tozig-out/bin/fx. That is the only binary that contains your latest change. -
When a user reports "still not working" after you believe you fixed something, do not assume they are running the wrong binary. Assume your fix is incomplete and investigate further. If you genuinely suspect a PATH mismatch, ask — do not silently copy binaries into
~/.fx/bin/. -
In any shell invocation — tmux, direct run, scripts — reference fx as
/Users/<you>/path/to/repo/zig-out/bin/fx(absolute) or./zig-out/bin/fx(when cwd is the repo root). Barefxis always wrong for dev verification.
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.
- today Changed · +7 lines · +120 tokens per session d05dc894b8f9
- 3d ago First seen · 462 lines · 5,829 tokens per session scan A 4aa25f96d96e
fx AGENTS.md is an instructions file published in the GitHub repository vercel-labs/fx (2,672 stars, last pushed today), licensed Apache-2.0. It adds 5,949 tokens to every session, about $0.0297 per session on Opus 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 2026-08-30.
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).
spec-kit AGENTS.md
AGENTS.md instructions for github/spec-kit, covering agents.md, about spec kit and specify, quickstart — add a new integration in 5 steps, integration architecture and integrationmanifest — file tracking.
codex AGENTS.md
AGENTS.md instructions for openai/codex, covering rust/codex-rs, the codex-core crate, code review rules, crate api surface and model visible context.
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 oss-third-party-notices.instructions.md
Instructions for microsoft/vscode, covering vs code oss third-party-notices pipeline, architecture, pipeline flow in ci, applying the notice (cutover) and fallback chain (never fail the build).
next.js AGENTS.md
Instructions for vercel/next.js, covering next.js development guide, codebase structure, monorepo overview, core package: packages/next and other important packages.