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 ymm-oss/fsl --skill fsl-requirementsgit clone --depth 1 https://github.com/ymm-oss/fslWrote 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/ymm-oss/fsl/fsl-requirements)<a href="https://agentmods.dev/skills/ymm-oss/fsl/fsl-requirements"><img src="https://agentmods.dev/badge/skills/ymm-oss/fsl/fsl-requirements.svg" alt="Measured on agentmods" 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 | $0.00085 | $0.02421 |
| Opus 5 | $0.00043 | $0.01210 |
| Sonnet 5 | $0.00017 | $0.00484 |
| Haiku 4.5 | $0.00009 | $0.00242 |
Grade A, and why
fsl-requirements 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 7d 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 — 162 lines — stays where its author put it; the contents beside it link to each section on GitHub.
FSL Requirements Layer
Use this skill to formalize PM/PdM requirements as a requirements Name { ... }
FSL file. The deliverable is a requirements contract that development can consume:
requirement IDs, source text, operations, guards, acceptance criteria, forbidden
flows, and optional conformance to an upper business layer.
Before writing syntax, read ../fsl/SKILL.md, then use its reference index to
load only the needed language and verifier detail. When working inside this
repository, read examples/pm/, examples/layers/return_system.fsl, and
examples/e2e/2_requirements.fsl for the requirements dialect. Read
examples/nfr/ only when SLA/deadline behavior is in scope.
Faithfulness gate (definition of done)
The two failures this layer exists to prevent are dropping a requirement (a thin spec) and inventing a rule the source never stated. Hold both ends:
- Cover the source. Every requirement in the document maps to at least one transition / invariant / acceptance / forbidden, or is recorded in the memo as out-of-scope or needs-decision. The step-1 coverage map forces the hard requirements in instead of stopping at the happy path.
- Ground the spec. Every declaration carries provenance — process
covers REQ-CHECKOUT-001 "..."to source text, or the typed annotation@requirement("REQ-CHECKOUT-001", "...")on a declaration that links to an ID arequirementblock owns, with aMODEL-/ASSUME-prefixed id for an explicit modeling choice. Those two are the canonical forms (docs/DESIGN-id-policy.md); the"REQ-1: text"string slot is non-canonical migration input, so never write it. An untagged declaration is an ungrounded guess, not a style nit. - Do not invent to reach green. If
check/verifyneeds a guard, bound, state, actor, deadline, or exception the source does not state, that is a step-1 question for the human — not a default you may pick to reachverified. - Make it mechanical.
fslc check <file> --strict-tagsflags everyuntaggeddeclaration (an invented rule) and everyunreferenced_requirement(a requirement nothing checks); done = zero of both. Add--requirements <ids>(the memo's source-ID list) to also catch requirements omitted entirely. Keep provenance in the.fslas tags, not a separate file.
What ships with it
1 file 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.
- 7d ago First seen · 162 lines · 85 tokens per session scan A 2f4a5723a857
fsl-requirements is a skill published in the GitHub repository ymm-oss/fsl (23 stars, last pushed 2d ago), licensed Apache-2.0. It adds 85 tokens to every session and 2,421 once invoked, about $0.0004 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.
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