fx is a command-line coding agent written in Zig, designed to run like a Unix tool and to be embedded in larger systems. Developers use it to work with language models through local or cloud inference providers. The catalogue instruction extends its coding-agent workflow.
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 skills add vercel-labs/fx --skill fx-cli-shapegit clone --depth 1 https://github.com/vercel-labs/fxWrote 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/skills/vercel-labs/fx/fx-cli-shape)<a href="https://agentmods.dev/skills/vercel-labs/fx/fx-cli-shape"><img src="https://agentmods.dev/badge/skills/vercel-labs/fx/fx-cli-shape/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/skills/vercel-labs/fx/fx-cli-shape"><img src="https://agentmods.dev/badge/skills/vercel-labs/fx/fx-cli-shape.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 | $0.00175 | $0.03528 |
| Opus 5.5 | $0.00070 | $0.01411 |
| Sonnet 5.5 | $0.00035 | $0.00706 |
| Haiku 4.5 | $0.00017 | $0.00353 |
Grade A, and why
fx-cli-shape 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 4d 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 — 104 lines — stays where its author put it; the contents beside it link to each section on GitHub.
fx CLI shape
fx follows git and Unix conventions for how people and scripts control it. Each concept gets one mechanism and one name, so anyone who knows git can guess the command, flag, or setting. Use this skill to pick the mechanism for a new control, name it on every surface, and check a change before it lands. The maintainers agreed on these rules; follow them unless a maintainer says otherwise in the conversation.
Current versus target
One piece the rules rely on isn't built yet: the Experimental section of /settings. Design new work toward them, but never tell a user to run something that doesn't exist yet. Check ./zig-out/bin/fx help and ./zig-out/bin/fx <command> --help when unsure. When a target piece is missing, use the nearest current pattern and say what's missing.
Decision order
Ask in order and stop at the first yes:
- Is it an action? Use a subcommand, named as a verb or a noun plus a verb. Inside a session, a slash command with the same name.
- Is it what the action works on? Use an argument.
- Is it a secret? Use the credential store, with an env var only for CI. Never a flag, which shows up in
psand shell history, and never.fx.json. - Does it matter for this run only? Use a flag.
- Should it persist? Use a setting, plus a flag with the same name for one-off overrides.
- Is it safe for an untrusted repo to set, and useful for a team to share? It may also be project-safe in
.fx.json, with a maintainer's approval. - Is it set by CI, a wrapper, a terminal, debugging, or tests? Use an env var in the right namespace.
- Is it unfinished? Use an
experimental.<name>setting.
Core rules
These are the rules agents most often get wrong. references/rules.md has the full set, with what's built today.
Extend before adding. Before adding a command, flag, setting, or env var, check whether extending an existing command or control covers the need, for example a scope flag on fx usage instead of a new fx stats. Every new control is a promise that costs a deprecation to take back. When a new one is still the right call, say why the existing one can't be extended.
What ships with it
3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 4d ago Changed 298ab403cd0a
- 6d ago First seen · 104 lines · 175 tokens per session scan A dafff6b1a52f
fx-cli-shape is a skill published in the GitHub repository vercel-labs/fx (3,762 stars, last pushed yesterday), licensed Apache-2.0. It adds 175 tokens to every session and 3,528 once invoked, about $0.0007 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 2026-11-01.
fx-cli-shape compared with skills from other repositories
| Mod | Type | Stars | Last push | Licence | Scan | Tokens | Works with |
|---|---|---|---|---|---|---|---|
| fx-cli-shapevercel-labs/fx | Skill | 3.8k | yesterday | Apache-2.0 | A | 175 | Claude Code, Codex |
| imagegenopenai/codex | Skill | 133k | yesterday | Apache-2.0 | A | 113 | Codex |
| playwright-climicrosoft/playwright | Skill | 99k | yesterday | Apache-2.0 | A | 19 | Claude Code |
| local-ai-agentsmicrosoft/ai-agents-for-beginners | Skill | 79k | 4d ago | MIT | A | 200 | Claude Code, Codex |
| systematic-debuggingobra/superpowers | Skill | 313k | 3d ago | MIT | A | 21 | Claude Code |
| next-cache-components-adoptionvercel/next.js | Skill | 143k | yesterday | MIT | A | 95 | Claude Code |
| next-partial-prefetching-adoptionvercel/next.js | Skill | 143k | yesterday | MIT | A | 103 | Claude Code |