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/thrixel/build-worldnpx agentmods add skills/thrixel/build-world/skill-authoringWrote 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/thrixel/build-world/skill-authoring)<a href="https://agentmods.dev/skills/thrixel/build-world/skill-authoring"><img src="https://agentmods.dev/badge/skills/thrixel/build-world/skill-authoring/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/thrixel/build-world/skill-authoring"><img src="https://agentmods.dev/badge/skills/thrixel/build-world/skill-authoring.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 | $0.00249 | $0.01503 |
| Opus 5.5 | $0.00100 | $0.00601 |
| Sonnet 5.5 | $0.00050 | $0.00301 |
| Haiku 4.5 | $0.00025 | $0.00150 |
Grade A, and why
skill-authoring 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 1mo 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.
This is a copy
95% identical to unreal-skill — 6 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 — 113 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Agent Skill Authoring
You are authoring an Unreal Engine Agent Skill: a named, reusable bundle of instructions that packages essential knowledge the agent either doesn't know or needs to pay close attention to. A skill can provide general best practices in a domain, guidance on a specific workflow, or a mix of both.
Principles
A good skill is:
Novel: The content should be things the agent doesn't already know or can't learn by using tools. If the agent could figure it out by calling a tool, don't put it in a skill.
Collegial: Write like you're briefing a knowledgeable colleague, not authoring documentation. Assume the reader understands Unreal. Give them what they need to act, not a full explanation of how everything works.
Flexible: Skills can include conceptual explanations, step-by-step instructions, or a mix. Use whichever form makes the guidance clearest for the task.
Durable: Don't embed property names, tool names, or other details that change over time. Skills that reference specific API names break silently when those names change.
Agnostic: Don't reference orchestration systems, role names, model names, or anything about how the agent is wired up. Skills should work regardless of the surrounding infrastructure.
Parsimonious: Every token costs context. Put them where they matter most and cut anything that isn't essential or evergreen. If a sentence wouldn't be missed, remove it.
Before You Write
Work through these questions before writing anything.
1. Does the skill already exist? Call ListSkills via MCP to see all registered skills in the project, then GetSkills on anything relevant. If the capability is already covered, point the user to the existing skill rather than creating a new one.
2. Choose the implementation path. Two paths exist and the choice depends on where the skill lives:
- Python class: The right choice when the skill is part of a code plugin. It lives alongside the plugin's Python toolsets, is version-controlled with the plugin, and is registered automatically when the plugin loads.
- UAsset: The right choice when the skill is project-specific and doesn't belong in a plugin. Create it directly in the Content Browser using
CreateSkillvia MCP. No code required.
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.
- 1mo ago First seen · 113 lines · 249 tokens per session scan A 372a41d5e9da
skill-authoring is a skill published in the GitHub repository thrixel/build-world (108 stars, last pushed 9d ago), licensed Apache-2.0. It adds 249 tokens to every session and 1,503 once invoked, about $0.0010 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 95% identical to unreal-skill, differing in 6 lines, and is treated as a copy.
skill-authoring compared with skills from other repositories
| Mod | Type | Stars | Last push | Licence | Scan | Tokens | Works with |
|---|---|---|---|---|---|---|---|
| skill-authoringthrixel/build-world | Skill | 108 | 9d ago | Apache-2.0 | A | 249 | Claude Code |
| scenario-blender-retopologyscenario-labs/skills | Skill | 3.2k | yesterday | MIT | A | 131 | Claude Code |
| scenario-godot-expertscenario-labs/skills | Skill | 3.2k | yesterday | MIT | A | 139 | Claude Code |
| scenario-roblox-toolingscenario-labs/skills | Skill | 3.2k | yesterday | MIT | A | 179 | Claude Code |
| scenario-blender-hairscenario-labs/skills | Skill | 3.2k | yesterday | MIT | A | 116 | Claude Code |
| scenario-maya-retopology-uvscenario-labs/skills | Skill | 3.2k | yesterday | MIT | A | 138 | Claude Code |
| scenario-zbrush-expertscenario-labs/skills | Skill | 3.2k | yesterday | MIT | A | 124 | Claude Code |