Hi Product Hunt, I'm Nick. I build integrations and AI agents for small service businesses, and testing them has always meant choosing between a client's live books, an empty vendor sandbox, or mocks that only return what you expected. fieldtwin is what I wanted instead. It runs the Jobber and QuickBooks Online APIs on your laptop, backed by a believable fake business that lives in both systems at once. Your code changes one URL and works against it as it would against the real thing. Then you can make it hard: throttle QuickBooks, lose the answer to a write, send a webhook twice, jump the clock past every token's expiry. Afterwards, get the exact list of what your code or agent changed, and rewind it. It's modeled from the vendors' public docs, and FIDELITY.md says how closely, behavior by behavior. It's free, Apache 2.0, and not affiliated with Jobber or Intuit. I'd love to know which system you'd want twinned next.

fieldtwin

Jobber and QuickBooks APIs on your laptop, for safe testing

Jobber and QuickBooks APIs on your laptop, for safe testing