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 agentmods add skills/quangphu1912/codebase-analyzer/detect-hidden-contractsnpx skills add quangphu1912/codebase-analyzer --skill detect-hidden-contractsgit clone --depth 1 https://github.com/quangphu1912/codebase-analyzerWrote 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/quangphu1912/codebase-analyzer/detect-hidden-contracts)<a href="https://agentmods.dev/skills/quangphu1912/codebase-analyzer/detect-hidden-contracts"><img src="https://agentmods.dev/badge/skills/quangphu1912/codebase-analyzer/detect-hidden-contracts.svg" alt="Measured on agentmods" 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 | $0.00036 | $0.01159 |
| Opus 5 | $0.00018 | $0.00580 |
| Sonnet 5 | $0.00007 | $0.00232 |
| Haiku 4.5 | $0.00004 | $0.00116 |
Grade A, and why
detect-hidden-contracts 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 3d 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 — 83 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Announce at start: "Using codebase-analyzer to detect hidden contracts."
Overview
Find implicit contracts not documented in types, interfaces, or API schemas. These are the assumptions that code makes but never states — where real bugs and hidden behaviors live. Every codebase has them: runtime expectations that compile-time checks can't catch, sequencing rules that nothing enforces, data shapes that code assumes but never validates. These hidden contracts are the gap between what the code says it does and what it actually requires.
Boundary with inventorying-api-surface
API surface (inventorying-api-surface) finds implicit ENTRY POINTS (how you get in). This skill finds implicit BEHAVIORAL ASSUMPTIONS (what the code assumes about how it's used). Same codebase, different lens. API surface maps the doors; hidden contracts maps the load-bearing walls that nobody drew on the blueprint.
Five Contract Types
1. Environment Variable Contracts
Code reads process.env.X without validation, defaults, or existence checks. The contract: "this variable will always be set in production." When it isn't, behavior ranges from silent wrong answers to crashes.
Detection: Search for process.env. usage without accompanying ||, ??, or if (!process.env.X) guards. Also check os.Getenv, os.environ.get, and similar in other languages.
Interrogation pattern: "What breaks when these ENV vars don't exist? Which ones are required vs optional? Which ones change behavior silently vs fail loudly?"
2. Ordering Contracts
Function A must be called before function B, but nothing enforces the sequence. Typically manifests as shared mutable state: a global variable set in one function and read in another, or an initialization step that must precede usage.
Detection: Search for shared mutable state, global variables set in one function and read in another, singletons that require explicit initialization, state machines with implicit transitions.
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.
- 3d ago First seen · 83 lines · 36 tokens per session scan A b93e69ad5c47
detect-hidden-contracts is a skill published in the GitHub repository quangphu1912/codebase-analyzer (2 stars, last pushed 4mo ago), licensed MIT. It adds 36 tokens to every session and 1,159 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 2026-08-31.
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