new-spec

new-spec is a skill for Claude Code, Codex from ymm-oss/fsl. It costs 36 tokens per session (296 once invoked), scanned A, original, Apache-2.0.

A guided workflow for writing or substantially changing an FSL specification. FSL is a formal specification language used to describe and check how software should behave.

In plain words
What is it for?
Use it to check, verify, test, mutate, and assess whether a new or changed FSL specification is meaningful.
Why use it?
It reduces the risk of accepting a specification that has syntax errors, misses counterexamples, or does not actually constrain behavior.

Skill for Claude CodeCodex

Install

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.

agentmods
npx agentmods add skills/ymm-oss/fsl/new-spec
Any agent
npx skills add ymm-oss/fsl --skill new-spec
Clone the repo
git clone --depth 1 https://github.com/ymm-oss/fsl

Made for: Claude Code, Codex.

Wrote 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.

agentmods badge for new-spec

README.md
[![agentmods](https://agentmods.dev/badge/skills/ymm-oss/fsl/new-spec.svg)](https://agentmods.dev/skills/ymm-oss/fsl/new-spec)
Your own site
<a href="https://agentmods.dev/skills/ymm-oss/fsl/new-spec"><img src="https://agentmods.dev/badge/skills/ymm-oss/fsl/new-spec.svg" alt="Measured on agentmods" height="20"></a>
Per session 36 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 296 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00036 $0.00296
Opus 5 $0.00018 $0.00148
Sonnet 5 $0.00007 $0.00059
Haiku 4.5 $0.00004 $0.00030

Measured 4d ago against content hash 50e9c1c0e0e6, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

new-spec 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.

.claude/skills/new-spec/SKILL.md · 29 lines

What it actually says

Author a meaningful FSL spec

Read skills/fsl/SKILL.md and only its relevant topical reference before writing syntax. Use the working-tree native prefix:

cargo run --manifest-path rust/Cargo.toml -p fslc-rust --bin fslc --

Gate

  1. check <spec> for syntax and semantic diagnostics.
  2. verify <spec> --depth 8 or a justified bound for bounded evidence.
  3. verify <spec> --engine induction when the intended claim is unbounded.
  4. mutate <spec> to measure whether properties constrain behavior.
  5. verify <spec> --vacuity error where applicable.
  6. Run the focused corpus/command test required by the spec's dialect or example family.

Do not hollow out a spec to dodge a counterexample. Confirm source requirements and exceptions before inventing behavior. Keep confirmed assumptions with the spec using established metadata. If FSL is the wrong tool for the behavior, say so rather than forcing a vacuous model.

Changing a corpus file may affect contract or compatibility artifacts. Use their owning generator only after confirming the semantic change is intentional; never hand-edit a snapshot.

Changes

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.

  1. 4d ago First seen · 29 lines · 36 tokens per session scan A 50e9c1c0e0e6

Subscribe to this mod's changes

new-spec is a skill published in the GitHub repository ymm-oss/fsl (23 stars, last pushed today), licensed Apache-2.0. It adds 36 tokens to every session and 296 once invoked, about $0.0002 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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