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 monkilabs/opencastle --skill writing-for-agentsgit clone --depth 1 https://github.com/monkilabs/opencastleWrote 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/monkilabs/opencastle/writing-for-agents)<a href="https://agentmods.dev/skills/monkilabs/opencastle/writing-for-agents"><img src="https://agentmods.dev/badge/skills/monkilabs/opencastle/writing-for-agents/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/monkilabs/opencastle/writing-for-agents"><img src="https://agentmods.dev/badge/skills/monkilabs/opencastle/writing-for-agents.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00062 | $0.01807 |
| Opus 5 | $0.00031 | $0.00903 |
| Sonnet 5 | $0.00012 | $0.00361 |
| Haiku 4.5 | $0.00006 | $0.00181 |
Grade A, and why
writing-for-agents 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 5d 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 — 85 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Writing for Agents
Reference for any document an agent consumes: a skill, an instruction file, a doc reached by a pointer. The packaging differs, the writing does not. The same levers make each one predictable, because the agent takes the same process every run rather than producing the same output.
Context pointers
A context pointer is a reference held in the agent's context that names out-of-context material and encodes the condition for reaching it. A skill's description is one. The pointer's wording, not its target, decides when and how reliably the agent reaches the material. A must-have target behind a weakly worded pointer is a variance bug: sharpen the wording first, and inline the material only if sharpening fails.
A pointer does two jobs: state what the material is, and list the branches that should trigger reaching it. Every word costs on every turn, so it earns harder pruning than the body.
- Front-load the leading word. The pointer is where it does its triggering work.
- One trigger per branch. Synonyms renaming a single branch are one branch written twice.
- Cut identity the body already carries.
The two loads
Every document and pointer spends one of two budgets.
- Context load is the cost of always-loaded material on the agent's window. It spends tokens and attention whether or not it fires.
- Cognitive load is the cost on the human: which documents exist and when to reach for each. Not a cost to minimise, it is the price of human agency. Spend it where human judgement matters, remove it where it does not.
Material reached only through a pointer escapes context load at the price of the pointer's own line. Material with no pointer rides entirely on cognitive load.
Information hierarchy
A document is built from steps (ordered actions) and reference (definitions, rules, facts consulted on demand). The two mix freely. The core decision is where each piece sits on a ladder ranked by how immediately the agent needs it:
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.
- 5d ago First seen · 85 lines · 62 tokens per session scan A a4601ee7d479
writing-for-agents is a skill published in the GitHub repository monkilabs/opencastle (61 stars, last pushed 11d ago), licensed MIT. It adds 62 tokens to every session and 1,807 once invoked, about $0.0003 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 2026-09-03.
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