What is python-api-development?

Guidance for building Python web APIs with FastAPI or Flask, including authentication, input checking, and asynchronous endpoints that can handle waiting work efficiently.

Use it to create REST endpoints, define validated request models, add authentication, choose between FastAPI and Flask, and build asynchronous services.

It helps choose a framework and set up consistent validation, documentation, and request handling without designing every pattern from scratch.

python-api-development — Skill for Claude Code and Codex by justanesta

Install

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.

Any agent

npx skills add justanesta/claude-code-resources --skill python-api-development

Clone the repo

git clone --depth 1 https://github.com/justanesta/claude-code-resources

Made for: Claude Code, Codex.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/justanesta/claude-code-resources/python-api-development/github.svg)](https://agentmods.dev/skills/justanesta/claude-code-resources/python-api-development)

Your own site

<a href="https://agentmods.dev/skills/justanesta/claude-code-resources/python-api-development"><img src="https://agentmods.dev/badge/skills/justanesta/claude-code-resources/python-api-development/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/justanesta/claude-code-resources/python-api-development"><img src="https://agentmods.dev/badge/skills/justanesta/claude-code-resources/python-api-development.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 62 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 932 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

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	$0.00062	$0.00932
Opus 5.5	$0.00025	$0.00373
Sonnet 5.5	$0.00012	$0.00186
Haiku 4.5	$0.00006	$0.00093

Measured 2mo ago against content hash d30f9682282b, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

python-api-development 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 2mo 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.

skills/python/python-api-development/SKILL.md · 163 lines

How it starts

The opening of the file, as written. The whole thing — 163 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Python API Development

Modern patterns for building production-ready APIs with FastAPI and Flask.

Decision Matrix: FastAPI vs Flask

Factor	FastAPI	Flask	Winner
Performance	High (async)	Moderate	FastAPI
Auto docs	Built-in (OpenAPI)	Manual	FastAPI
Validation	Pydantic (automatic)	Manual/extensions	FastAPI
Learning curve	Steeper	Gentler	Flask for beginners
Async support	Native	With extensions	FastAPI

General guidance:

Use FastAPI when: New projects, async needed, want auto-docs, type safety important
Use Flask when: Simple apps, team knows Flask, sync-only fine, want simplicity

FastAPI Patterns

Basic API Structure

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    name: str
    price: float

@app.get("/")
def read_root():
    return {"message": "Hello World"}

@app.post("/items/")
def create_item(item: Item):
    return item

Pydantic Models for Validation

from pydantic import BaseModel, Field

class User(BaseModel):
    username: str = Field(..., min_length=3, max_length=50)
    email: str
    age: int = Field(..., ge=0, le=150)

See pydantic-validation.md for:

Custom validators
Model inheritance
Nested models

Dependency Injection

from fastapi import Depends

def get_db():
    db = Database()
    try:
        yield db
    finally:
        db.close()

@app.get("/items/")
def read_items(db = Depends(get_db)):
    return db.get_items()

See dependency-injection-patterns.md for:

Class-based dependencies
Dependency override (testing)
Sub-dependencies

Async Endpoints

@app.get("/data/")
async def get_data():
    async with httpx.AsyncClient() as client:
        response = await client.get("https://api.example.com/data")
        return response.json()

Read the full file on GitHub · 163 lines

Files

What ships with it

5 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

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.

2mo ago First seen · 163 lines · 62 tokens per session scan A d30f9682282b

Subscribe to this mod's changes

python-api-development is a skill published in the GitHub repository justanesta/claude-code-resources (2 stars, last pushed 6mo ago), licensed MIT. It adds 62 tokens to every session and 932 once invoked, about $0.0002 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 2026-08-31.

Backend and APIs Languages Python

python-api-development