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.
git clone --depth 1 https://github.com/iloveitaly/llm-ide-rulesWrote 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/rules/iloveitaly/llm-ide-rules/fastapi)<a href="https://agentmods.dev/rules/iloveitaly/llm-ide-rules/fastapi"><img src="https://agentmods.dev/badge/rules/iloveitaly/llm-ide-rules/fastapi/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/rules/iloveitaly/llm-ide-rules/fastapi"><img src="https://agentmods.dev/badge/rules/iloveitaly/llm-ide-rules/fastapi.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 | $0.00000 | $0.00243 |
| Opus 5.5 | $0.00000 | $0.00097 |
| Sonnet 5.5 | $0.00000 | $0.00049 |
| Haiku 4.5 | $0.00000 | $0.00024 |
Grade A, and why
fastapi 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 2d 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.
What it actually says
Fastapi
- Raise
ClientError(app.routes.errors) instead ofHTTPException. See theClientErrordocstring for further instructions and usage. - Do not return a
dict, instead create aclass RouteNameResponse- Locate these classes right above the
def route_name():function which uses them.
- Locate these classes right above the
- Use
Model.onewhen a record must exist in order for the business logic to succeed. - Do not try/except
Model.onewhen using a parameter from the request to pull a record. Let this exception bubble up. - Use
model_id: Annotated[TypeID, Path()]to represent a model ID as a URL path parameter - Use the typed route helpers in
app/generated/fastapi_typed_routes.pyfor all URL generation. - User-facing errors must not name internals. 3rd party API errors (Stripe, Clerk, etc) or internal implementation jargon should exist in error messages displayed to the browser. Think hard about user-facing error messages and make it clear what the user should do next.
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.
- 2d ago Changed 7c83c66cb9eb
- 23d ago Changed · -1 lines 0040a40b67cf
- 29d ago Changed · +1 lines 77942234e52f
- 1mo ago First seen · 16 lines · 0 tokens per session scan A 35ef0f64aa1a
fastapi is a cursor rule published in the GitHub repository iloveitaly/llm-ide-rules (13 stars, last pushed 2d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 243 tokens. 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 2026-08-30.
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