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 xobotyi/cc-foundry --skill output-style-engineeringgit clone --depth 1 https://github.com/xobotyi/cc-foundryWrote 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/xobotyi/cc-foundry/output-style-engineering)<a href="https://agentmods.dev/skills/xobotyi/cc-foundry/output-style-engineering"><img src="https://agentmods.dev/badge/skills/xobotyi/cc-foundry/output-style-engineering.svg" alt="Measured on agentmods" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to medium
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- medium Rogue Agent · line 132 Skill establishes unauthorized persistence across sessions via cron jobs, startup scripts, or state files. Session persistence allows an attacker to maintain access beyond the current interaction.Fix: Remove any persistence mechanisms (cron jobs, startup scripts, state files). Skills should not maintain state across sessions without explicit user consent.
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 | $0.00039 | $0.02959 |
| Opus 5 | $0.00019 | $0.01479 |
| Sonnet 5 | $0.00008 | $0.00592 |
| Haiku 4.5 | $0.00004 | $0.00296 |
Grade A, and why
output-style-engineering 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 8d 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 — 177 lines — stays where its author put it; the contents beside it link to each section on GitHub.
An output style modifies the system prompt. It holds two powers no alternative has: it turns part of the default prompt off, and the harness reinforces it with adherence reminders through the conversation. Every other file-based mechanism only adds text, and then competes with the default it could not remove.
Choose the mechanism first
- Use a style when the role or the register must change and hold for a whole session. The body lives in the system prompt, so it survives compaction, and the harness reminders carry adherence without persistence prose in the body.
- Additive mechanisms stay additive. CLAUDE.md arrives as a user message after the system prompt, and
--append-system-promptappends for one session; neither removes the default the body is arguing with. A body that would work identically as CLAUDE.md content is not a style. - Route the rest away. A rule that must never break belongs in a hook — prose steers, the lifecycle mechanism enforces. A procedure a user invokes belongs in a skill. Work that needs an isolated context belongs in a subagent: a style governs the main conversation only, and a subagent runs its own system prompt, while a fork inherits the parent's prompt with the style included.
- A style shapes Claude's prose, not tool output. Bash output, file contents, and MCP results reach the user unchanged, so a format complaint about them is never a style defect.
# Tone and styleis never removable — the conciseness rule and the no-emoji rule included. A style that must beat those defaults states the behavior it wants, specifically enough that the more general default has nothing to contest. Specificity is what wins; a blanket precedence clause is not — see Never claim precedence over the prompt.
File format, frontmatter fields including force-for-plugin, storage paths and nested resolution, activation methods,
scope priority, the built-in catalog, the comparison against related features, and Agent SDK integration:
[${CLAUDE_SKILL_DIR}/references/spec.md]. Read it when writing the file, deciding where it lives, or loading a style
through the SDK.
What ships with it
7 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.
- 8d ago First seen · 177 lines · 39 tokens per session scan A ab157a3346bd
output-style-engineering is a skill published in the GitHub repository xobotyi/cc-foundry (20 stars, last pushed yesterday), licensed MIT. It adds 39 tokens to every session and 2,959 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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