Getting it into your agent
This one installs as part of its plugin. Adding the marketplace and installing the plugin brings it with everything else the plugin ships.
/plugin marketplace add int2t05/engineering-skills/plugin install engineering-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/int2t05/engineering-skills/deprecation-migration)<a href="https://agentmods.dev/skills/int2t05/engineering-skills/deprecation-migration"><img src="https://agentmods.dev/badge/skills/int2t05/engineering-skills/deprecation-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/int2t05/engineering-skills/deprecation-migration"><img src="https://agentmods.dev/badge/skills/int2t05/engineering-skills/deprecation-migration.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00078 | $0.01987 |
| Opus 5 | $0.00039 | $0.00993 |
| Sonnet 5 | $0.00016 | $0.00397 |
| Haiku 4.5 | $0.00008 | $0.00199 |
Grade A, and why
deprecation-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 9d 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 — 139 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Deprecation and Migration
Code is a liability, not an asset. Every line carries maintenance cost — bugs, dependency updates, security patches, onboarding overhead. Deprecation is the discipline of removing code that no longer earns its keep; migration is the process of moving users safely from old to new. Most organizations build things well; few remove them well.
Hyrum's Law makes removal hard: with enough users, every observable behavior becomes depended on — including bugs, timing quirks, and undocumented side effects. Deprecation therefore requires active migration, not just announcement. Plan removal at design time — systems with clean interfaces, feature flags, and minimal surface area are far easier to sunset.
When to use
- Replacing an old system, API, or library with a new one.
- Sunsetting a feature that's no longer needed, or consolidating duplicate implementations.
- Removing dead code that nobody owns but everybody depends on.
- Planning the lifecycle of a new system (deprecation planning starts at design time).
- Deciding whether to maintain a legacy system or invest in migration.
- Upgrading a dependency or framework version, including major/breaking upgrades (see
references/dependency-upgrade.md). - Moving data between systems (dual-write, backfill, CDC, cutover) — see
references/data-migration.md.
Not for: patching a security vulnerability in place (use security-review); routine commits (use git-workflow).
Steps
1. Make the deprecation decision
Before deprecating anything, answer:
- Does this system still provide unique value? If yes, maintain it.
- How many consumers depend on it? Quantify the migration scope.
- Does a replacement exist? If no, build the replacement first — never deprecate without an alternative.
- What's the migration cost for each consumer? Trivially automated → do it; manual and high-effort → weigh against maintenance cost.
- What's the ongoing cost of not deprecating? Security risk, engineer time, opportunity cost of complexity.
What ships with it
3 files 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.
- 9d ago First seen · 139 lines · 78 tokens per session scan A 1aad218ece5f
deprecation-migration is a skill published in the GitHub repository int2t05/engineering-skills (3 stars, last pushed 8d ago), licensed MIT. It adds 78 tokens to every session and 1,987 once invoked, about $0.0004 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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