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 agentmods add skills/markus-global/markus/skill-buildingnpx skills add markus-global/markus --skill skill-buildinggit clone --depth 1 https://github.com/markus-global/markusWhat 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 | $0.00019 | $0.03392 |
| Opus 5 | $0.00010 | $0.01696 |
| Sonnet 5 | $0.00004 | $0.00678 |
| Haiku 4.5 | $0.00002 | $0.00339 |
Grade A, and why
skill-building 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 3d 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 — 257 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Skill Building
This skill teaches you how to create Markus skill packages — directory-based artifacts that teach agents new capabilities. A skill can work in two ways (or both):
- Instruction-based: A
SKILL.mdfile with instructions injected into the agent's context, guiding it to use existing tools in new ways. - MCP-based: A bundled MCP server (script) that provides entirely new tools to the agent. The skill directory can contain any scripts, config files, or resources the MCP server needs.
Most skills are instruction-based. Use MCP-based skills when the capability requires new tools that don't exist yet (e.g., connecting to an external API, browser automation, hardware control).
Artifact Directory
CRITICAL: Skill artifacts MUST be saved under this exact path — the Builder page, install system, and deliverable detection all depend on it:
~/.markus/builder-artifacts/skills/{skill-name}/
├── skill.json # Manifest (auto-created from your JSON output)
├── SKILL.md # Instruction document (you write via file_write)
├── README.md # Human-readable documentation (optional)
├── images/ # Skill icon images (optional)
│ └── icon.png # Skill icon — used in UI after install
└── ... # Any other files: scripts, MCP servers, configs, templates, etc.
Do NOT write artifacts to ~/.markus/shared/, your working directory, or any other location. Only ~/.markus/builder-artifacts/skills/ is recognized by the system.
A skill directory can contain any files needed for the skill to work — not just SKILL.md and README.md. For example:
- MCP server scripts (e.g.,
server.mjs) that provide new tools to the agent - Configuration templates or data files
- Helper scripts used by the instructions
When the user installs the artifact, the entire directory (all files) is deployed to ~/.markus/skills/{skill-name}/. SKILL.md is loaded and injected into the agent's context when the skill is activated. If the manifest declares mcpServers, those servers are started and their tools registered to the agent. skill.json contains metadata used by the skill registry. README.md provides documentation for humans browsing or sharing the skill.
What ships with it
1 file 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.
- 3d ago First seen · 257 lines · 19 tokens per session scan A 7966475d5834
skill-building is a skill published in the GitHub repository markus-global/markus (157 stars, last pushed 6d ago), licensed Apache-2.0. It adds 19 tokens to every session and 3,392 once invoked, about $0.0001 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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