Getting it into your agent
It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.
git clone --depth 1 https://github.com/ArchAstro/archagentsnpx agentmods add skills/archastro/archagents/build-skillWrote 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/archastro/archagents/build-skill)<a href="https://agentmods.dev/skills/archastro/archagents/build-skill"><img src="https://agentmods.dev/badge/skills/archastro/archagents/build-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/archastro/archagents/build-skill"><img src="https://agentmods.dev/badge/skills/archastro/archagents/build-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 | $0.00071 | $0.01539 |
| Opus 5.5 | $0.00028 | $0.00616 |
| Sonnet 5.5 | $0.00014 | $0.00308 |
| Haiku 4.5 | $0.00007 | $0.00154 |
Grade A, and why
build-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 2mo 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.
Copies of this mod
1 near-identical copy found in the catalogue:
- archagent-build-skill — 94% identical, 4 lines differ
How it starts
The opening of the file, as written. The whole thing — 167 lines — stays where its author put it; the contents beside it link to each section on GitHub.
ArchAstro Skill Builder
Create, edit, and publish skills — reusable instruction packages that agents invoke at runtime.
This skill assumes the ArchAgent CLI is already installed and authenticated. Use the /archagents:install and /archagents:auth commands in this same plugin instead of trying to install or authenticate the CLI manually inside this skill.
What is a Skill?
A skill is a file-backed bundle anchored by a SKILL.md root file with optional supporting files. Skills use the same managed virtual-path model as scripts and workflows: skills live under skills/<slug>/..., scripts under scripts/..., and workflows under workflows/.... Agents invoke skills at runtime via the get_skill tool to load instructions on demand.
Always Start with State
Every invocation must begin by understanding the current context:
archagent auth status
archagent list skills
Determine whether the user wants to:
- create a brand-new skill,
- edit an existing skill,
- or inspect a skill before modifying it.
Routing
User wants to create a new skill
Walk through the authoring flow step by step.
-
Gather requirements:
- What should the skill do? (purpose and scope)
- What trigger phrases should activate it? (for the description field)
- Does it need supporting files (templates, schemas, reference docs)?
- Which agent(s) will use it?
-
Choose a slug: Short, lowercase, hyphen-separated identifier (e.g.,
order-lookup,weekly-report). This becomes the skill's permanent key. -
Author the SKILL.md file locally:
Create a directory structure:
skills/<slug>/ ├── SKILL.md # Root file (required) └── references/ # Optional supporting files └── example.mdThe SKILL.md must have YAML frontmatter:
--- name: <skill-name> description: <One-line description with trigger phrases. Be specific — this is how the agent decides when to invoke the skill. Include phrases like "use when...", "trigger phrases include..."> --- # Skill Title Detailed instructions for the agent...
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.
- 2mo ago First seen · 167 lines · 71 tokens per session scan A 429960eb0324
build-skill is a skill published in the GitHub repository ArchAstro/archagents (7 stars, last pushed 29d ago), licensed MIT. It adds 71 tokens to every session and 1,539 once invoked, about $0.0003 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 2026-08-31.
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