basst¶

Pydantic-first HTTP testing client for Python. Fluent request builder, one-step model binding, native Python assertions.

The name comes from des basst -- southern German dialect for "that fits" or "that's as expected."

Install¶

pip install basst

Or with uv:

uv add basst

Quick Start¶

from basst import Client, matchers
from pydantic import BaseModel


class User(BaseModel):
    id: int
    name: str
    email: str
    roles: list[str]


api = Client("https://api.example.com")

user = (
    api.get("/users/1")
    .header("X-Token", "secret")
    .expect()
    .status(200)
    .header("content-type", matchers.contains("json"))
    .model(User)
)

assert user.name == "Ada"
assert "admin" in user.roles

Features¶

• Fluent, chainable request builder (all HTTP verbs)
• Pydantic model binding with .model() and .model_list()
• Automatic content-type validation before parsing
• Built-in header matchers (equals, contains, starts_with, ends_with, matches)
• Custom matchers via simple callables
• Async support (await only at .expect())
• Contextual error messages with request/response details
• from_httpx for wrapping existing httpx clients

Next: User Guide for the full API.