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 cyanheads/census-mcp-server --skill add-skillgit clone --depth 1 https://github.com/cyanheads/census-mcp-serverWrote 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/cyanheads/census-mcp-server/add-skill)<a href="https://agentmods.dev/skills/cyanheads/census-mcp-server/add-skill"><img src="https://agentmods.dev/badge/skills/cyanheads/census-mcp-server/add-skill/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/cyanheads/census-mcp-server/add-skill"><img src="https://agentmods.dev/badge/skills/cyanheads/census-mcp-server/add-skill.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 | $0.00095 | $0.02523 |
| Opus 5.5 | $0.00038 | $0.01009 |
| Sonnet 5.5 | $0.00019 | $0.00505 |
| Haiku 4.5 | $0.00010 | $0.00252 |
Grade A, and why
add-skill 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.
This is a copy
100% identical to add-skill — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 139 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Context
A server has two skill trees, written for different readers:
| Tree | Reader | Written by |
|---|---|---|
framework-skills/ |
The agent building the server | init and the maintenance sync, plus any development skills of the server's own |
skills/ (root) |
The agent that installed the server and is calling its tools | The author, deliberately |
Root skills/ is absent by default; init and maintenance never write it. Claude Code always scans a plugin's root skills/ (Agent Plugins 1.0.0 fixes discovery there), so no skills field is needed in .claude-plugin/plugin.json. Each SKILL.md follows the Agent Skills specification; a host skips one that doesn't, without a word, which is why lint:packaging validates the tree.
No skill by default
Publish one only when an agent calling the tools needs something instructions and tool descriptions cannot carry: a multi-hop identifier chain, a gate that prevents a wrong call or a wrong conclusion, a query syntax. Overview skills that restate the tool list, generic "how to use this server" workflows, and skills for hypothetical tasks do not ship.
Authoring rules
- Perspective. The reader is the agent calling the server's tools in the middle of a multi-step task, not the maintainer. Walk a realistic workflow against the tool surface and write down what that agent needs at each hop.
- One skill per server, split by trigger. The description stays resident in every session; the body loads only on invocation, so workflows belong inside the one skill, not in a second with the same trigger. A second skill earns its place only when a distinct trigger vocabulary routes to a materially different workflow. Two is the cap; three when day-to-day use of the server proves it.
- Naming. Default
<package short name>-guide(pubmed-guideforpubmed-mcp-server). The description names the tool prefix (pubmed_*) so the agent binds the skill to the tools it sees. - Layering. Tool
.describe()text carries the per-tool contract;instructionscarries a one-paragraph orientation (canonical chain, identifier types, rate posture); MCP prompts stay user-invoked task templates. The skill carries what none of those can: when to reach for the server and when not to, where each opaque identifier comes from, gates, branching workflows, and syntax references. It never restatesinstructions. - Gates are the section a skill exists for. Each is an imperative the agent satisfies before acting or concluding: a precondition (resolve a name to an ID before filtering, where an unresolved filter returns the global set), a stop rule (confirm coverage before reporting a record absent), or a confirmation gate (ask the user before a tool that sends, writes, or deletes). Verified facts only, sourced from
instructions, the design doc's Workflow Analysis and Known Limitations, tool descriptions, or closed issues — nothing invented. Cut any fact that would not change what the agent does. - Drift. Name tools in prose; never list their parameters — the schemas own them.
- Budget.
SKILL.mdunder 150 lines (the specification's 500 is a ceiling, not a target); the description under 500 characters, since it is resident in every session. Long material goes toreferences/.
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 · 139 lines · 95 tokens per session scan A 0d4497574def
add-skill is a skill published in the GitHub repository cyanheads/census-mcp-server (2 stars, last pushed yesterday), licensed Apache-2.0. It adds 95 tokens to every session and 2,523 once invoked, about $0.0004 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 100% identical to add-skill, differing in 0 lines, and is treated as a copy.
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