skills-x: Skill for Claude Code

.claude/skills/writing-plans/SKILL.md

writing-plans is a skill for Claude Code from castle-x/skills-x. It costs 21 tokens per session (795 once invoked), scanned A, a copy of writing-plans, MIT.

A skill for writing detailed implementation plans before changing code. The plan explains the files, tests, documentation, and small development steps needed for a multi-step task.

In plain words
What is it for?
Use it when you have a specification or requirements for a larger change. It saves the plan under docs/plans with a dated feature name and includes implementation, testing, and commit steps.
Why use it?
It gives an engineer who is new to the codebase enough context to carry out the work consistently. Breaking work into small actions makes testing and progress easier to follow.

Skill for Claude Code

Written for Claude Code: installed under .claude/. Also seen: mentions subagents.

This is castle-x/skills-x's own configuration. It tells Claude Code how to work on skills-x itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything skills-x configures →

Reuse

Borrowing it

Nothing to install: this file belongs to castle-x/skills-x. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file
curl -O https://raw.githubusercontent.com/castle-x/skills-x/main/.claude/skills/writing-plans/SKILL.md
Clone the repo
git clone --depth 1 https://github.com/castle-x/skills-x

Made for: Claude Code.

Wrote this? Show the measurements

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README.md
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agentmods 80×15 button for writing-plans

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Per session 21 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 795 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin 100% copy Near-identical to another mod 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 5.1 $0.00021 $0.00795
Opus 5.5 $0.00008 $0.00318
Sonnet 5.5 $0.00004 $0.00159
Haiku 4.5 $0.00002 $0.00080

Measured 2mo ago against content hash 8a9198d4d9ef, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

writing-plans 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 2mo 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.

Origin

This is a copy

100% identical to writing-plans — 4 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

.claude/skills/writing-plans/SKILL.md · 117 lines

How it starts

The opening of the file, as written. The whole thing — 117 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Writing Plans

Overview

Write comprehensive implementation plans assuming the engineer has zero context for our codebase and questionable taste. Document everything they need to know: which files to touch for each task, code, testing, docs they might need to check, how to test it. Give them the whole plan as bite-sized tasks. DRY. YAGNI. TDD. Frequent commits.

Assume they are a skilled developer, but know almost nothing about our toolset or problem domain. Assume they don't know good test design very well.

Announce at start: "I'm using the writing-plans skill to create the implementation plan."

Context: This should be run in a dedicated worktree (created by brainstorming skill).

Save plans to: docs/plans/YYYY-MM-DD-<feature-name>.md

Bite-Sized Task Granularity

Each step is one action (2-5 minutes):

  • "Write the failing test" - step
  • "Run it to make sure it fails" - step
  • "Implement the minimal code to make the test pass" - step
  • "Run the tests and make sure they pass" - step
  • "Commit" - step

Plan Document Header

Every plan MUST start with this header:

# [Feature Name] Implementation Plan

> **For Claude:** REQUIRED SUB-SKILL: Use superpowers:executing-plans to implement this plan task-by-task.

**Goal:** [One sentence describing what this builds]

**Architecture:** [2-3 sentences about approach]

**Tech Stack:** [Key technologies/libraries]

---

Task Structure

### Task N: [Component Name]

**Files:**
- Create: `exact/path/to/file.py`
- Modify: `exact/path/to/existing.py:123-145`
- Test: `tests/exact/path/to/test.py`

**Step 1: Write the failing test**

```python
def test_specific_behavior():
    result = function(input)
    assert result == expected
```

**Step 2: Run test to verify it fails**

Run: `pytest tests/path/test.py::test_name -v`
Expected: FAIL with "function not defined"

**Step 3: Write minimal implementation**

```python
def function(input):
    return expected
```

**Step 4: Run test to verify it passes**

Run: `pytest tests/path/test.py::test_name -v`
Expected: PASS

**Step 5: Commit**

```bash
git add tests/path/test.py src/path/file.py
git commit -m "feat: add specific feature"
```

Read the full file on GitHub · 117 lines

Files

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.

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. 2mo ago First seen · 117 lines · 21 tokens per session scan A 8a9198d4d9ef

Subscribe to this mod's changes

writing-plans is a skill published in the GitHub repository castle-x/skills-x (18 stars, last pushed 11d ago), licensed MIT. It adds 21 tokens to every session and 795 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 100% identical to writing-plans, differing in 4 lines, and is treated as a copy.

Related

writing-plans compared with skills from other repositories

writing-plans next to 6 skills from other repositories
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writing-planscastle-x/skills-xSkill1811d agoMITA21Claude Code
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