cassette-sdk 0.1.1

One-call shim to route LLM SDK traffic through the Cassette record/replay gateway

cassette-sdk

Record/replay LLM & agent API calls so your tests run fast, free, and deterministic.

The first time your tests run, Cassette records each LLM response to a local file. After that it replays the saved response — no network, no API key, no token cost, and no random failures from the model wording things differently.

Install

pip install cassette-sdk

Use (in-process, no gateway)

from cassette.recorder import http_client
from openai import OpenAI

client = OpenAI(http_client=http_client(project="demo"))  # records → replays locally

Modes via CASSETTE_MODE: record | replay | auto (default). Cassettes are plain JSON in ./.cassettes and diff cleanly in PRs.

Detect real regressions

from cassette.drift import compare_cassette_files
result = compare_cassette_files("baseline.json", "new.json")
print(result.verdict)  # identical | benign | regression

It ignores harmless rewording but flags changed tool calls, structured-output shape changes, and truncation as regressions.

Free and open source (MIT). Team features (shared registry + GitHub PR merge-gate) at cassette.dev.