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 Cristhianzl/claude-skills-czl --skill developing-featuresgit clone --depth 1 https://github.com/Cristhianzl/claude-skills-czlWrote 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/cristhianzl/claude-skills-czl/developing-features)<a href="https://agentmods.dev/skills/cristhianzl/claude-skills-czl/developing-features"><img src="https://agentmods.dev/badge/skills/cristhianzl/claude-skills-czl/developing-features/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/cristhianzl/claude-skills-czl/developing-features"><img src="https://agentmods.dev/badge/skills/cristhianzl/claude-skills-czl/developing-features.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 | $0.00116 | $0.02869 |
| Opus 5 | $0.00058 | $0.01435 |
| Sonnet 5 | $0.00023 | $0.00574 |
| Haiku 4.5 | $0.00012 | $0.00287 |
Grade A, and why
developing-features 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 7d 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 — 180 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Developing Features
Production code. Secure by default, structured by responsibility, simple until proven otherwise.
Read first (always)
List learnings/ and read every file relevant to the current task. Project-specific conventions, banned patterns, or security constraints live there and override the defaults in this SKILL.md. If a learning conflicts with this file, the learning wins — mention it to the user.
Tradeoff — when to apply, when to lighten up
Apply the full discipline when the code is production-bound, multi-user, or persists state. Lighten the formality (still keep security and naming) when the code is a one-off script, a throwaway exploration, or a sample under 50 lines. Don't impose SRP/DIP/file-structure ceremony on a 10-line CLI helper.
Pre-implementation check (mandatory)
Before writing any code, answer these six questions:
- What am I trusting here that I haven't verified? External inputs, tokens, signatures, IDs, flags, headers — anything from outside.
- What is the blast radius if this goes wrong? Can an attacker read other users' data? Forge events? Execute arbitrary operations? Exhaust resources?
- Am I implementing this from the authoritative source? Official docs, official SDK, official spec — not a tutorial, not a copy-paste.
- What happens in the failure path? Does a failed check silently succeed? Does an exception get swallowed? Does the error leak internals?
- Who controls this value, and can they lie? Client-sent fields can be forged. Headers can be spoofed. If you don't control it, you don't trust it.
- What platforms must this run on, and have I assumed POSIX where it isn't guaranteed? Paths, shell, fork, signals, encoding — see
ensuring-cross-platform.
If any answer is "I don't know" → stop, find out, then continue.
The reuse ladder (before writing any code)
The best code is the code you never wrote. Walk down the ladder and stop at the first rung that answers — be lazy about the solution, never about reading (trace the real code first):
What ships with it
8 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.
- 7d ago Changed 5615a8affb90
- 11d ago First seen · 180 lines · 116 tokens per session scan A ed3904826caf
developing-features is a skill published in the GitHub repository Cristhianzl/claude-skills-czl (5 stars, last pushed today), licensed MIT. It adds 116 tokens to every session and 2,869 once invoked, about $0.0006 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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