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-verifygit 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-verify)<a href="https://agentmods.dev/skills/ymm-oss/fsl/fsl-verify"><img src="https://agentmods.dev/badge/skills/ymm-oss/fsl/fsl-verify/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-verify"><img src="https://agentmods.dev/badge/skills/ymm-oss/fsl/fsl-verify.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 | $0.00169 | $0.04016 |
| Opus 5.5 | $0.00068 | $0.01606 |
| Sonnet 5.5 | $0.00034 | $0.00803 |
| Haiku 4.5 | $0.00017 | $0.00402 |
Grade A, and why
fsl-verify 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 — 185 lines — stays where its author put it; the contents beside it link to each section on GitHub.
FSL Verify — choose the run, read the result, report the claim
This skill owns verification: which fslc commands a spec needs, how to read
their JSON without over-reading it, how to repair from the output, and how to
report what was and was not shown. The layer skills keep only their minimal
check loop and point here. For syntax read ../fsl/SKILL.md; the full command
catalog is ../fsl/references/commands.md and the repair table per result
kind is ../fsl/references/errors.md.
Three facts drive everything below:
- Exit 0 is not "passed". Several outputs that matter (
deadlockandunreferenced_requirementwarnings,difffindings,mutatesurvivors,not_evaluatedseams) arrive with exit 0. Read the fields named in the tables, not only the exit code. - Every claim has a scope.
verifiedis bounded by--depth.provedholds for theverify { instances / values }sizes it ran at, and the envelope does not repeat those sizes — you must. - Undecided is not a pass.
unknown_cti,unknown_budget,not_evaluated,not_run, andclosure: falsemean the question is still open.
1. Decision table — which commands, in which order
Run the "required" column in order and stop at the first non-pass; repair (§4) and re-run from the top of the column. "When relevant" items are part of the job when the condition holds, not optional extras.
| Input | Change | Required, in order | When relevant |
|---|---|---|---|
business |
new | check → lint → verify --depth 8 → verify --engine induction |
As-Is/To-Be: refine tobe.fsl asis.fsl map.fsl; strength: mutate --depth 4 --by-requirement |
requirements |
new | check --strict-tags --requirements ids.txt → lint → verify --depth 8 (read implements.result) → verify --engine induction → scenarios |
strength: mutate --by-requirement; NFR deadline: a tighter deadline must fail |
design (kernel spec) |
new | check → lint → verify --depth 8 → verify --engine induction → refine design.fsl req.fsl map.fsl |
unknown_cti: --lemma or --engine explicit (§3); strength: mutate; handoff: testplan / testgen |
| any spec | edit of an existing spec | the column for its layer, then diff old.fsl new.fsl --forbid behavior_added,behavior_removed,invariant_weakened,forbidden_relaxed,unknown (or diff --git BASE..HEAD --forbid ...) |
refine again against the unchanged upper layer; mutate kill rate against the previous baseline |
| several layers | any | chain fsl-project.toml |
deepen only the failing layer with its own column |
| implementation | write or fix code | testgen or testplan → run the implementation's tests → replay |
never lower --depth to make generated tests pass |
| failure that depends on size | any | sweep --depth 1..8 --instances E=1..3 |
counterexample export for the minimal case |
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.
- today First seen · 185 lines · 169 tokens per session scan A 87bd0da571ef
fsl-verify is a skill published in the GitHub repository ymm-oss/fsl (33 stars, last pushed today), licensed Apache-2.0. It adds 169 tokens to every session and 4,016 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 2026-10-17.
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