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-from-codegit 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-from-code)<a href="https://agentmods.dev/skills/ymm-oss/fsl/fsl-from-code"><img src="https://agentmods.dev/badge/skills/ymm-oss/fsl/fsl-from-code/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/ymm-oss/fsl/fsl-from-code"><img src="https://agentmods.dev/badge/skills/ymm-oss/fsl/fsl-from-code.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00112 | $0.02303 |
| Opus 5.5 | $0.00045 | $0.00921 |
| Sonnet 5.5 | $0.00022 | $0.00461 |
| Haiku 4.5 | $0.00011 | $0.00230 |
Grade A, and why
fsl-from-code 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 — 165 lines — stays where its author put it; the contents beside it link to each section on GitHub.
FSL From Code — extracting a design spec from an implementation
Use this skill when the input is existing code and the deliverable is an FSL
design-layer spec. The direction is the reverse of fsl-design: there is no
upper requirements contract to refine to, so the spec is anchored downward —
its faithfulness is proved by replaying the generated conformance harness against
the very code it was read from. That conformance harness is this skill's seam:
the downward analogue of a refinement seam, a contract checked against real code
rather than against an upper spec. If the user later wants an upper requirements
contract, building that upward refinement seam is fsl-design's job, not this
skill's.
Before writing syntax, read ../fsl/SKILL.md, then use its reference index to
load only the needed language rules, verifier workflow, and repair detail. The
artifact this skill produces is the usual spec-first triple read in reverse:
plain code → a kernel spec whose actions and invariants each carry a
// SRC: file:line witness (and // ASSUME-n: for every bound or modeling
choice) → the fslc testgen Adapter + random-walk Monitor harness that checks
the code against the spec.
Boundary
Produce only:
- A design-layer kernel
specwhose state/actions/guards/effects are read from the code, each tagged with a// SRC: file:linewitness - Invariants and forbidden flows that the human confirmed, tagged with
// ASSUME-n:ledger comments - The
fslc testgenconformance harness, with the Adapter wired to the real code
Do not:
- Invent invariants, guards, states, or transition targets to make the spec look complete or to make it verify. A missing rule is a question, not a default.
- Produce a requirements or business layer, or refine upward.
- Claim implementation conformance unless the harness actually ran green against the
code (a spec that only
verifys is internally consistent, not faithful to code).
Why this is not a transpiler — three zones
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 · +2 lines 3f465480ea34
- 1mo ago First seen · 163 lines · 112 tokens per session scan A 86372d597fd2
fsl-from-code is a skill published in the GitHub repository ymm-oss/fsl (33 stars, last pushed today), licensed Apache-2.0. It adds 112 tokens to every session and 2,303 once invoked, about $0.0004 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 2026-08-30.
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