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 Threat-Vector-Security/guardian-agent --skill deprecation-and-migrationgit clone --depth 1 https://github.com/Threat-Vector-Security/guardian-agentWrote 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/threat-vector-security/guardian-agent/deprecation-and-migration)<a href="https://agentmods.dev/skills/threat-vector-security/guardian-agent/deprecation-and-migration"><img src="https://agentmods.dev/badge/skills/threat-vector-security/guardian-agent/deprecation-and-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/threat-vector-security/guardian-agent/deprecation-and-migration"><img src="https://agentmods.dev/badge/skills/threat-vector-security/guardian-agent/deprecation-and-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 | $0.00045 | $0.01902 |
| Opus 5 | $0.00023 | $0.00951 |
| Sonnet 5 | $0.00009 | $0.00380 |
| Haiku 4.5 | $0.00005 | $0.00190 |
Grade A, and why
deprecation-and-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.
This is a copy
89% identical to deprecation-and-migration — 43 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 207 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Deprecation and Migration
Overview
Code is a liability, not an asset. Every line of code has ongoing maintenance cost — bugs to fix, dependencies to update, security patches to apply, and new engineers to onboard. Deprecation is the discipline of removing code that no longer earns its keep, and migration is the process of moving users safely from the old to the new.
Most engineering organizations are good at building things. Few are good at removing them. This skill addresses that gap.
When to Use
- Replacing an old system, API, or library with a new one
- Sunsetting a feature that's no longer needed
- 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
Core Principles
Code Is a Liability
Every line of code has ongoing cost: it needs tests, documentation, security patches, dependency updates, and mental overhead for anyone working nearby. The value of code is the functionality it provides, not the code itself. When the same functionality can be provided with less code, less complexity, or better abstractions — the old code should go.
Hyrum's Law Makes Removal Hard
With enough users, every observable behavior becomes depended on — including bugs, timing quirks, and undocumented side effects. This is why deprecation requires active migration, not just announcement. Users can't "just switch" when they depend on behaviors the replacement doesn't replicate.
Deprecation Planning Starts at Design Time
When building something new, ask: "How would we remove this in 3 years?" Systems designed with clean interfaces, feature flags, and minimal surface area are easier to deprecate than systems that leak implementation details everywhere.
The Deprecation Decision
Before deprecating anything, answer these questions:
1. Does this system still provide unique value?
→ If yes, maintain it. If no, proceed.
2. How many users/consumers depend on it?
→ Quantify the migration scope.
3. Does a replacement exist?
→ If no, build the replacement first. Don't deprecate without an alternative.
4. What's the migration cost for each consumer?
→ If trivially automated, do it. If manual and high-effort, weigh against maintenance cost.
5. What's the ongoing maintenance cost of NOT deprecating?
→ Security risk, engineer time, opportunity cost of complexity.
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 · 207 lines · 45 tokens per session scan A bf2d9b4e3bc6
deprecation-and-migration is a skill published in the GitHub repository Threat-Vector-Security/guardian-agent (13 stars, last pushed yesterday), licensed Apache-2.0. It adds 45 tokens to every session and 1,902 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. It is 89% identical to deprecation-and-migration, differing in 43 lines, and is treated as a copy.
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