Braintrust

Braintrust is an AI evaluation and observability platform for builders who are past the toy demo stage. It gives you a place to log traces, build datasets, run experiments, compare prompt and model changes, and inspect what an agent did when it called tools or failed a task.

For a technical solo founder, the value is discipline. Instead of changing prompts by feel, you can save representative tasks, rerun them, and see whether the new version actually improved. That matches the lesson that keeps showing up in production agent talks: the hard part is not making an impressive first run, it is knowing whether the next hundred runs are safe, cheaper, and better.

The free Starter plan makes Braintrust worth testing early. The paid Pro tier starts high enough that most solos should wait until evals are tied to revenue, support quality, or customer-facing automation. If you are building agents that send emails, operate tools, or affect customers, Braintrust belongs on the shortlist. If you are still manually prompting ChatGPT for one-off work, it is too much machinery.