MetaClaw idempotent-script-design

Use this skill when writing scripts, cron jobs, data pipelines, or any automated process that may be run multiple times. Design every operation to be safely re-runnable without side effects.

install

source · Clone the upstream repo

git clone https://github.com/aiming-lab/MetaClaw

Claude Code · Install into ~/.claude/skills/

T=$(mktemp -d) && git clone --depth=1 https://github.com/aiming-lab/MetaClaw "$T" && mkdir -p ~/.claude/skills && cp -r "$T/memory_data/skills/idempotent-script-design" ~/.claude/skills/aiming-lab-metaclaw-idempotent-script-design && rm -rf "$T"

manifest: memory_data/skills/idempotent-script-design/SKILL.md

source content

Idempotent Script Design

An idempotent operation produces the same result whether run once or ten times.

Techniques:

Check before create:
```
CREATE TABLE IF NOT EXISTS
```
,
```
mkdir -p
```
, check file existence before writing.
Upsert instead of insert: Use
```
INSERT ... ON CONFLICT DO UPDATE
```
in SQL.
Atomic writes: Write to a temp file, then rename — prevents corrupt partial output.
Track progress: Write a completion marker or checkpoint so reruns skip done work.

Testing idempotency: Run your script twice on the same input and verify the output is identical.

Anti-patterns:

Appending to a file without checking if the data is already there.
Inserting rows without checking for duplicates.