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 igmarin/rails-agent-skills --skill review-migrationgit clone --depth 1 https://github.com/igmarin/rails-agent-skillsWrote 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/igmarin/rails-agent-skills/review-migration)<a href="https://agentmods.dev/skills/igmarin/rails-agent-skills/review-migration"><img src="https://agentmods.dev/badge/skills/igmarin/rails-agent-skills/review-migration/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/igmarin/rails-agent-skills/review-migration"><img src="https://agentmods.dev/badge/skills/igmarin/rails-agent-skills/review-migration.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00040 | $0.01043 |
| Opus 5 | $0.00020 | $0.00522 |
| Sonnet 5 | $0.00008 | $0.00209 |
| Haiku 4.5 | $0.00004 | $0.00104 |
Grade A, and why
review-migration 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 11d 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 — 115 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Review Migration
Use this skill when schema changes must be safe in real environments.
HARD-GATE
DO NOT combine schema change and data backfill in one migration.
DO NOT add NOT NULL on a column that hasn't been fully backfilled.
DO NOT drop columns before all code references are removed.
Core Process
- Identify the database and table-size risk.
- Separate schema changes from data backfills.
- Check lock behavior for indexes, constraints, defaults, and rewrites.
- Plan deployment order between app code and migration code.
- Plan rollback or forward-fix strategy.
If the project uses strong_migrations, follow it. If it does not, apply the same safety rules manually.
Safe Patterns and Common Mistakes
| Operation | Safe Pattern | Common Mistake | Why It Fails |
|---|---|---|---|
| Add column | Nullable first, backfill later, enforce NOT NULL last | add_column :t, :col, :string, null: false, default: "x" on large table |
Table rewrite + lock (PG < 11) |
| Add index (large table) | algorithm: :concurrently (PG) / :inplace (MySQL) + disable_ddl_transaction! |
add_index :users, :email without algorithm: :concurrently |
Share lock blocks writes |
| Backfill data | Batch job outside migration transaction, throttle to reduce replication lag | User.update_all(...) inside migration |
Transaction lock held for full duration |
| Rename column | Add new, copy data, migrate callers, drop old | Rename column directly | Breaks running app during deploy |
| Add NOT NULL | After backfill confirms all rows have values | Enforce NOT NULL before backfill completes | Fails or locks on rows missing values |
| Add foreign key | After cleaning orphaned records | Add FK without cleaning orphans | Constraint violation at migration time |
| Remove column | Remove code references first, deploy, then drop column | Drop column while code still reads it | unknown attribute errors at runtime |
For every step, state the expected lock or table-rewrite risk explicitly; if negligible, say why.
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.
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.
- 11d ago First seen · 115 lines · 40 tokens per session scan A a7bbed189a64
review-migration is a skill published in the GitHub repository igmarin/rails-agent-skills (25 stars, last pushed 20d ago), licensed MIT. It adds 40 tokens to every session and 1,043 once invoked, about $0.0002 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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