Mistral Next Playground for Prompt Testing

This Mistral Next playground is a UI for prompt testing and evals on a preview/early model—so you can measure behavior changes before adopting it in production.

Pre-adoption evaluation: regression tests, side-by-side comparisons with the stable model you ship today, and quick checks for formatting and instruction-following.

Yes. Bring your API keys. LangFast routes requests through our proxy.

To keep the playground stable (abuse prevention + rate limits) and to let you save runs, compare deltas, and share results with your team.

Use a fixed regression suite: your strictest formatting prompts, your most failure-prone edge cases, and your “must-pass” examples from production.

Behavior drift: outputs may change between updates. This is exactly why you should run repeatable eval prompts before switching.

Yes. Run the same prompt set side-by-side and inspect differences in quality, safety behavior, and formatting compliance.

Yes. Use rubric scoring (clarity, correctness, structure) and track pass/fail on strict format checks to see if it’s truly better.

Yes. Preview models can break formatting unexpectedly—use eval prompts that enforce your output contract.

Yes. If your product relies on multi-turn behavior, create a repeatable conversation script and rerun it across versions.

Yes. Inject real examples (tickets, policies, product data) so you’re not benchmarking on toy prompts.

Yes—export to cURL/JS/JSON so engineering can reproduce the exact request and parameters.

Yes. Save runs for auditability and share links for review or rollout decisions.

LangFast is free to use with some basic features. You need to provide your own API keys to run models and use the app. When you add your API keys, you pay the model provider (e.g., OpenAI) for the credits/tokens you use. LangFast premium features can be unlocked with a one-time purchase.

Wait for reset or add paid usage to keep running preview evaluations.

We stream responses through a lightweight proxy. Speed depends on Mistral Next and load; compare latency across models directly.

No. We don’t train on your prompts or data. Sharing is opt-in and retention is configurable.

Requests route to model providers. See the Data & Privacy page for processing regions and details.

LangChain helps you build systems. LangFast helps you evaluate preview model behavior before you implement or migrate.

Those tools manage datasets and evals inside pipelines. LangFast is the quickest way to run interactive regression tests and compare preview vs stable models.