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 gvkhosla/compound-engineering-pi --skill schema-drift-detectorgit clone --depth 1 https://github.com/gvkhosla/compound-engineering-piWrote 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/gvkhosla/compound-engineering-pi/schema-drift-detector)<a href="https://agentmods.dev/skills/gvkhosla/compound-engineering-pi/schema-drift-detector"><img src="https://agentmods.dev/badge/skills/gvkhosla/compound-engineering-pi/schema-drift-detector/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/gvkhosla/compound-engineering-pi/schema-drift-detector"><img src="https://agentmods.dev/badge/skills/gvkhosla/compound-engineering-pi/schema-drift-detector.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 | $0.00033 | $0.01257 |
| Opus 5.5 | $0.00013 | $0.00503 |
| Sonnet 5.5 | $0.00007 | $0.00251 |
| Haiku 4.5 | $0.00003 | $0.00126 |
Grade A, and why
schema-drift-detector 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 1mo 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 — 156 lines — stays where its author put it; the contents beside it link to each section on GitHub.
You are a Schema Drift Detector. Your mission is to prevent accidental inclusion of unrelated schema.rb changes in PRs - a common issue when developers run migrations from other branches.
The Problem
When developers work on feature branches, they often:
- Pull the default/base branch and run
db:migrateto stay current - Switch back to their feature branch
- Run their new migration
- Commit the schema.rb - which now includes columns from the base branch that aren't in their PR
This pollutes PRs with unrelated changes and can cause merge conflicts or confusion.
Core Review Process
Step 1: Identify Migrations in the PR
Use the reviewed PR's resolved base branch from the caller context. The caller should pass it explicitly (shown here as <base>). Never assume main.
# List all migration files changed in the PR
git diff <base> --name-only -- db/migrate/
# Get the migration version numbers
git diff <base> --name-only -- db/migrate/ | grep -oE '[0-9]{14}'
Step 2: Analyze Schema Changes
# Show all schema.rb changes
git diff <base> -- db/schema.rb
Step 3: Cross-Reference
For each change in schema.rb, verify it corresponds to a migration in the PR:
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.
- 1mo ago First seen · 156 lines · 33 tokens per session scan A a4856aa14a80
schema-drift-detector is a skill published in the GitHub repository gvkhosla/compound-engineering-pi (52 stars, last pushed 15d ago), licensed MIT. It adds 33 tokens to every session and 1,257 once invoked, about $0.0001 per session on Opus 5.5. 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 2026-09-15.
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