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 oborchers/fractional-cto --skill api-designgit clone --depth 1 https://github.com/oborchers/fractional-ctoWrote 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/oborchers/fractional-cto/api-design)<a href="https://agentmods.dev/skills/oborchers/fractional-cto/api-design"><img src="https://agentmods.dev/badge/skills/oborchers/fractional-cto/api-design/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/oborchers/fractional-cto/api-design"><img src="https://agentmods.dev/badge/skills/oborchers/fractional-cto/api-design.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 | $0.00101 | $0.02462 |
| Opus 5.5 | $0.00040 | $0.00985 |
| Sonnet 5.5 | $0.00020 | $0.00492 |
| Haiku 4.5 | $0.00010 | $0.00246 |
Grade A, and why
api-design 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 — 202 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Define Your Public API Surface and Defend It
The public API is the contract between your library and every downstream user. Once a symbol is public, removing or changing it is a breaking change. Getting the boundary right -- what is exported, what is private, how errors are communicated, how complexity is layered -- is the most consequential design decision in a Python library. Get it wrong and you end up like Pydantic v1: an unintentionally wide API surface that required a full rewrite to fix.
httpx is the gold standard. Every public symbol is re-exported from __init__.py. Every implementation module is underscore-prefixed (_client.py, _config.py). The exception hierarchy is a carefully designed tree. Sync and async clients share all non-I/O logic in a _BaseClient. Study httpx before designing your own API.
Public API Surface: __all__ and Underscore Modules
Every module that exports symbols must define __all__. This documents intent, controls from module import *, and tells tools (mypy, pyright, mkdocstrings) what is public.
| Rule | Rationale |
|---|---|
Define __all__ in every public module |
Documents the contract; tools rely on it |
Re-export everything from __init__.py |
Users write from mylib import Client, never from mylib._client import Client |
Prefix all implementation modules with _ |
_client.py, _config.py, _exceptions.py make the private boundary unambiguous |
Sort __all__ alphabetically |
Easy to review in diffs, easy to check for completeness |
Include type aliases and protocols in __all__ |
Users need them for type-checking; easy to forget |
| Bad | Good |
|---|---|
from mylib.client import Client |
from mylib import Client |
No __all__, everything implicitly public |
Explicit __all__ listing every public name |
utils.py with mixed public/private helpers |
_utils.py for internal, re-export public helpers from __init__.py |
Expose less than you think you need. You can always make something public later; you cannot easily make it private. If it is in __all__, it is a contract. If it starts with an underscore, you can change it freely.
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 · 202 lines · 101 tokens per session scan A 7db606554d9b
api-design is a skill published in the GitHub repository oborchers/fractional-cto (32 stars, last pushed 3d ago), licensed MIT. It adds 101 tokens to every session and 2,462 once invoked, about $0.0004 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 2026-10-13.
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