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 aayushostwal/nexus --skill skill-writergit clone --depth 1 https://github.com/aayushostwal/nexusWrote 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/aayushostwal/nexus/skill-writer)<a href="https://agentmods.dev/skills/aayushostwal/nexus/skill-writer"><img src="https://agentmods.dev/badge/skills/aayushostwal/nexus/skill-writer.svg" alt="Measured on agentmods" 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 | $0.00072 | $0.01898 |
| Opus 5 | $0.00036 | $0.00949 |
| Sonnet 5 | $0.00014 | $0.00380 |
| Haiku 4.5 | $0.00007 | $0.00190 |
Grade A, and why
nexus-skill-writer-md 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 8d 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 — 192 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Nexus Skill Writer
Produce a complete, production-ready skill every session — not a draft, not a skeleton.
Required Directory Layout
skill-name/
├── SKILL.md ← entry point, <500 lines
├── checklists/
│ └── execution-checklist.md
├── anti-patterns/
│ └── common-mistakes.md
└── validation/
└── output-validation.md
Every SKILL.md must have YAML frontmatter:
---
name: nexus-{skill-name} # kebab-case, unique, descriptive
description: > # THE TRIGGER MECHANISM — be explicit and dense
Use this skill when ... [detailed trigger conditions].
Trigger phrases include: "...", "...", "...".
Also trigger when ... [edge cases].
When in doubt, use this skill.
---
The description is the single most important field. Claude selects skills based only on name + description. A vague description means the skill never triggers. Under-triggering is the #1 skill failure mode.
Phase 0 — Skill Classification
Before writing anything, classify the request:
New skill or extension?
- Scan
available_skillsin the system prompt. - If an existing skill covers 60%+ of the use case, offer to extend instead.
- Present options as a table:
| Option | Best when | Risk |
|---|---|---|
| Extend existing | Same domain, similar triggers | May bloat the existing skill |
| Create new | Distinct triggers, different output contract | Maintenance overhead |
| Merge two skills | Overlapping triggers, narrow scopes | Wider scope per skill |
Never decide for the user — present options and wait for direction.
Category:
| Category | Description |
|---|---|
| engineering | Code generation, architecture, implementation |
| debugging | Failure investigation, root cause, regression |
| devops | CI/CD, infra, deployments |
| code-review | PR review, diff analysis, quality checks |
| testing | Test writing, coverage, test strategy |
| reliability | SLOs, on-call, incident management |
| observability | Logs, metrics, traces, dashboards |
| refactoring | Code transformation, technical debt |
| performance | Profiling, optimization, benchmarking |
What ships with it
2 files 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.
- 8d ago First seen · 192 lines · 72 tokens per session scan A c737882a5233
nexus-skill-writer-md is a skill published in the GitHub repository aayushostwal/nexus (18 stars, last pushed 29d ago), licensed MIT. It adds 72 tokens to every session and 1,898 once invoked, about $0.0004 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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