writing-plugins

A design guide for building add-ons made from reusable parts such as commands, agents, skills, and hooks. It explains how to choose those parts, arrange their files, and configure the plugin manifest for tools such as Claude Code or Codex CLI.

In plain words
What is it for?
Use it to plan or create a plugin, choose the right artifact for a user need, and set up its manifest and folders. It covers the corresponding plugin layouts for Claude Code, Codex CLI, and Antigravity.
Why use it?
It helps turn a collection of automation instructions into a correctly structured, installable add-on. It also reduces naming and configuration mistakes when the add-on targets more than one coding tool.

Skill for Claude CodeCodex

Part of the nlpm plugin — 17 skills, 12 commands, 8 agents, 1 hook shipped together

Install

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.

agentmods
npx agentmods add skills/xiaolai/nlpm/writing-plugins
Any agent
npx skills add xiaolai/nlpm --skill writing-plugins
Clone the repo
git clone --depth 1 https://github.com/xiaolai/nlpm

Made for: Claude Code, Codex.

Or install nlpm, the plugin that ships this one along with the rest of its 17 skills, 12 commands, 8 agents, 1 hook.

Per session 69 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,287 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00069 $0.03287
Opus 5 $0.00034 $0.01643
Sonnet 5 $0.00014 $0.00657
Haiku 4.5 $0.00007 $0.00329

Measured 3d ago against content hash bc7ae3e63a23, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

writing-plugins 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.

codex/skills/writing-plugins/SKILL.md · 394 lines

How it starts

The opening of the file, as written. The whole thing — 394 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Writing Plugins

Scope: covers plugin design and architecture. The examples use the Claude Code layout (.claude-plugin/plugin.json + auto-discovered commands/, agents/, skills/, hooks/). The same artifact-selection and architecture reasoning maps to the other tools — only the manifest path and packaging differ:

  • Codex CLI: .codex-plugin/plugin.json manifest + .agents/plugins/marketplace.json; skills live at .agents/skills/. See [[nlpm:conventions-codex]].
  • Antigravity: gemini-extension.json (becoming "Antigravity plugins"); skills at .agent/skills/. See [[nlpm:conventions-antigravity]].
  • Cross-tool skills: a SKILL.md collection with no plugin wrapper installs into any tool via npx skills add. See [[writing-skills]].

For individual artifact authoring, see [[writing-skills]], [[writing-agents]], [[writing-hooks]], [[writing-rules]].

1. Plugin = Commands + Agents + Skills + Hooks

A plugin is a collection of NL artifacts that work together. Before writing anything, decide which artifacts you need.

Artifact Selection Guide

User need Artifact Example
User runs a slash command Command /nlpm:score path/to/file.md
AI works autonomously on a task Agent Security scanner dispatched by a command
Domain knowledge for agents/Claude Skill SKILL.md with patterns and decision tables
Something must happen automatically on events Hook Lint-on-save, block force push
External service integration MCP server (.mcp.json) GitHub API, Slack notifications

Minimum Viable Plugin

The smallest useful plugin has one artifact:

my-plugin/
  .claude-plugin/
    plugin.json
  commands/
    do-thing.md

Don't add agents, skills, or hooks until you need them. Each artifact adds maintenance burden.

2. Architecture Patterns

Pattern: Single Command (simplest)

Command does everything itself. No agents, no orchestration.

Command receives input --> processes --> outputs result

Read the full file on GitHub · 394 lines

Changes

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.

  1. 3d ago First seen · 394 lines · 69 tokens per session scan A bc7ae3e63a23

Subscribe to this mod's changes

writing-plugins is a skill published in the GitHub repository xiaolai/nlpm (133 stars, last pushed 3d ago), licensed ISC. It adds 69 tokens to every session and 3,287 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 2026-08-30.

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