GPT-4o Playground for Prompt Testing

A GPT-4o vision playground is a UI for prompt testing and evals on image+text tasks using GPT-4o—so you can validate behavior before building a multimodal pipeline.

Prompt testing and evaluations for vision: extraction, classification, captioning, grounding, and structured outputs—run repeatedly on the same image set to measure consistency.

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

To prevent abuse, apply fair-use limits, and let you save runs, reuse test sets, and share results with your team.

Grounding accuracy (is it describing what’s actually there?), instruction following, sensitivity to ambiguous images, and stability across repeated runs.

Yes. Vision tasks often need strict output—use eval prompts that enforce schemas and measure how often formatting breaks.

Yes. Reuse the same image set to run regression tests and compare output drift across models and prompt changes.

Yes—run the same images and prompts side-by-side across providers to compare quality, cost, and latency.

Yes. Use prompts that force the model to say “unknown” when uncertain, and score how often it invents details that aren’t present.

Yes. Swap small prompt variations and measure changes in extraction accuracy and formatting compliance.

Yes—export to cURL/JS/JSON so your team can reproduce the exact call and parameters.

Yes. Save transcripts, keep prompt versions, and share links for review or sign-off.

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 continue running vision evals.

We stream responses via a lightweight proxy. Latency varies by GPT-4o and load; compare first-token time across models directly.

No. We don’t train on your prompts or files. 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 multimodal apps. LangFast helps you test vision prompts and evaluate outputs before you build.

Those tools manage datasets, evals, and tracing inside workflows. LangFast is the interactive bench to validate vision prompts and compare models quickly.