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/baleen37/bstack/write-skillnpx skills add baleen37/bstack --skill write-skillgit clone --depth 1 https://github.com/baleen37/bstackWhat 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 | $0.00052 | $0.00959 |
| Opus 5 | $0.00026 | $0.00479 |
| Sonnet 5 | $0.00010 | $0.00192 |
| Haiku 4.5 | $0.00005 | $0.00096 |
Grade A, and why
write-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 yesterday.
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 — 95 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Write Skills
Write the smallest SKILL.md that changes behavior. Most skills are one file with two frontmatter fields and a short body.
---
name: my-skill # lowercase-hyphens, matches the directory name
description: Use when ... # third person, names the trigger, <=1024 chars
---
The description is the whole trigger mechanism — it is all the model sees before deciding to load the skill. Say when to use it, using the words someone would actually type, and cover both failure directions ("triggers too rarely or too often", not just one). Never write "I help you..." .
For the body: include only what the model gets wrong without you. It knows the domain; it does not know your conventions or the traps. Cut anything else — a skill that restates common knowledge changes no behavior and costs context every session. Keep it under 500 lines, and write rules that hold for the whole task rather than one-time steps, because the body is injected once and never re-read.
Split to references/ only what a subset of runs needs, link it one level deep
from here, and say what is in it so the agent knows whether to open it.
Prove it works
Skip this and you are guessing. A new skill's baseline is the same task with no skill at all.
- Write 3+ tasks that show the failure, with a checkable success signal.
- Run them with no skill. That is the baseline.
- Write the smallest thing that fixes it.
- Re-run. Keep it only if it beats baseline.
If baseline already passes, do not write the general skill — say so. Then look for what the model cannot derive: your environment's facts, your conventions, the traps it knows in theory but misses under pressure. Either narrow the skill to that and re-test, or report that no skill is warranted. A skill that restates what baseline already did is pure context cost.
Match the testing to the stakes. A one-screen skill deserves a trigger check and one real task, not seven subagents.
Test the description separately: give a subagent the frontmatter only, with 5 prompts that should trigger and 4 that should not.
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.
- yesterday First seen · 95 lines · 52 tokens per session scan A c74a9d54847a
write-skill is a skill published in the GitHub repository baleen37/bstack (4 stars, last pushed 11d ago), licensed MIT. It adds 52 tokens to every session and 959 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 2026-08-31.
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