# Schema Diff

> Compare two schema states and surface the risky changes. Use before applying migrations or after a model change.

- Skill: `archive228/schema-diff` (Agent Skill)
- Install (CLI): `npx skillmds@latest add archive228/schema-diff`
- Raw SKILL.md: https://api.skillmd.com/api/skills/archive228/schema-diff/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: archive228 (https://skillmd.com/u/archive228)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/archive228/schema-diff

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# Schema Diff
Diff old vs new schema. Flag by risk:
- **Destructive** (high): dropped column/table, narrowed type, new NOT NULL on existing rows, dropped index a query relies on.
- **Locking** (high at scale): index without CONCURRENTLY, type change that rewrites the table.
- **Safe**: new nullable column, new table, new index CONCURRENTLY.
For each destructive change: is data lost? is it reversible? is there a backfill? Output a risk-ranked list and a go/no-go with the safe rollout order.