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 JakubMikolajek/codex-skills-collection --skill migration-strategygit clone --depth 1 https://github.com/JakubMikolajek/codex-skills-collectionWrote 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/jakubmikolajek/codex-skills-collection/migration-strategy)<a href="https://agentmods.dev/skills/jakubmikolajek/codex-skills-collection/migration-strategy"><img src="https://agentmods.dev/badge/skills/jakubmikolajek/codex-skills-collection/migration-strategy/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/jakubmikolajek/codex-skills-collection/migration-strategy"><img src="https://agentmods.dev/badge/skills/jakubmikolajek/codex-skills-collection/migration-strategy.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 | $0.00051 | $0.02565 |
| Opus 5 | $0.00026 | $0.01282 |
| Sonnet 5 | $0.00010 | $0.00513 |
| Haiku 4.5 | $0.00005 | $0.00257 |
Grade A, and why
migration-strategy 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 — 269 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Migration Strategy
A migration is a deployment. It modifies a shared, stateful system — the database — and unlike application code, it cannot simply be rolled back by reverting a deploy. This skill covers how to change database schemas safely without downtime and without data loss.
When to Use
- Planning a schema change to an existing production database
- Reviewing a migration file before it runs in production
- Designing the migration workflow for a CI/CD pipeline
- A migration ran but needs to be rolled back
- Adding a column or index to a large table in production
When NOT to Use
- Designing the initial schema for a new database — use
sql-and-database - Application-level data transformation logic not involving schema changes
- Message queue schema changes (different toolchain)
Core Principles
Migrations and Application Deployments are Separate
Never run a migration and deploy new application code simultaneously. Separate them into distinct, independently reversible steps. The application must be able to run against both the old and new schema during the transition window.
Expand-Contract Pattern
Every breaking schema change has a safe path: expand first (add new structure, keep old), deploy new application code that uses both, then contract (remove old structure once old code is gone). This eliminates downtime and enables rollback at every step.
Every Migration Must be Reversible — or Explicitly Not
Write a down migration for every up migration. If the down migration would cause data loss (e.g. dropping a column with data), document that explicitly and require sign-off before the migration runs in production. A migration with no rollback plan is a liability.
Migration Safety Classification
Before writing a migration, classify its risk:
| Operation | Risk | Strategy |
|---|---|---|
| Add nullable column | Safe | Deploy directly |
| Add column with default | Safe (Postgres 11+) | Deploy directly |
| Add index concurrently | Safe | CREATE INDEX CONCURRENTLY |
| Add foreign key | Medium | Add as NOT VALID, validate separately |
| Rename column | Breaking | Expand-contract (add new, migrate, remove old) |
| Drop column | Breaking | Expand-contract (remove from app first, then drop) |
| Change column type | Breaking | New column + backfill + swap + drop |
| Drop table | Breaking | Stop all references in app first, then drop |
| Add NOT NULL to existing column | Breaking | Backfill + add constraint with NOT VALID + validate |
| Large table backfill | Dangerous | Batch processing, never single transaction |
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 · 269 lines · 51 tokens per session scan A f4e7754e0279
migration-strategy is a skill published in the GitHub repository JakubMikolajek/codex-skills-collection (5 stars, last pushed 5d ago), licensed MIT. It adds 51 tokens to every session and 2,565 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 2026-08-31.
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