Gemini Prompt Tester — Test Gemini 2.5 Pro and Flash in Your Browser
freeprompttester.app is a free, browser-based prompt tester that talks to the Gemini API directly using your Google AI key. It supports Gemini 2.5 Pro, Gemini 2.5 Flash, and Gemini 2.0 Flash, and lets you compare any of them against Claude, GPT (via OpenRouter), Grok, Mistral, DeepSeek, Llama (Groq) and Cohere in the same run. Outputs stream into side-by-side cards with TTFT, latency, input/output tokens, and per-call cost. No sign-up, no proxy, no Freesuite servers in the request path.
Gemini models supported
| Model | Context | Input $/M | Output $/M | Best for |
|---|---|---|---|---|
| Gemini 2.5 Pro | 1M | $1.25 | $10 | Long context, reasoning, multimodal |
| Gemini 2.5 Flash | 1M | $0.30 | $2.50 | Fast, cheap, high volume |
| Gemini 2.0 Flash | 1M | $0.10 | $0.40 | Cheapest tier |
How to use Gemini in freeprompttester.app
- Get a free Google AI API key from
aistudio.google.com/app/apikey. - Open freeprompttester.app, click API keys, paste your key into the Google AI row, click Test.
- In the Models panel, switch to the Google AI tab and pick the Gemini variant you want.
- Write your prompt and hit Run. Streamed output appears in a card with cost calculated from Google's reported token counts.
Why test Gemini in a multi-provider tester?
Each model has a tokenization style and reasoning bias that show up immediately when you put outputs side by side. Gemini 2.5 Pro is exceptionally strong on long-document QA thanks to its 1M context window, but tends to be more verbose than Claude on the same prompt. Gemini 2.5 Flash is the most cost-effective fast model in this class. The only way to know whether Gemini fits your specific use case is to A/B it against the alternatives — freeprompttester.app makes that one click.
What "direct browser call" means for Gemini
The Gemini API supports ?key= query-string authentication and CORS, so freeprompttester.app calls generativelanguage.googleapis.com directly from your browser. No proxy server. You can verify by watching the Network tab while running a prompt — the only outbound request goes to Google's domain.
Multi-turn chat with Gemini
freeprompttester.app's Chat mode works seamlessly with Gemini 2.5 Pro and 2.5 Flash. The provider role mapping is handled automatically — Gemini uses user and model roles internally instead of user/assistant, and freeprompttester.app translates between them so multi-turn history serializes correctly. Open the Chat tab, pick Gemini 2.5 Flash (cheapest fast option), and have a parallel conversation alongside Claude or GPT to see how Gemini holds up across long context. Cumulative cost stays low because Gemini Flash is among the cheapest tier-1 chat models at $0.30 per 1M input tokens.
Synthesizing Gemini against other models
After running the same prompt against Gemini and a few competitors in single-shot mode, click ✦ Synthesize and pick Gemini 2.5 Pro (its 1M-token context handles the multi-response prompt comfortably) as the synthesizer. The combined answer + consensus + disagreement notes is a clean way to extract value from a multi-model run.
Try freeprompttester.app — Free, No Sign-Up
Bring your own API keys. Up to six models in parallel. Streams in your browser.
Open AI Prompt Tester →Frequently Asked Questions
Does Gemini support streaming in freeprompttester.app?
Yes. freeprompttester.app uses Gemini's streamGenerateContent endpoint with SSE, so tokens appear as they generate. TTFT is shown next to each card.
Where do I get a free Gemini API key?
Visit aistudio.google.com/app/apikey while signed in to a Google account. Free-tier keys give you generous Gemini 2.5 Flash quota plus paid Gemini 2.5 Pro access.
Why is my Gemini cost shown as $0.0000?
Gemini returns usage metadata at the end of the stream. If your prompt is very short and the response is also short, the displayed cost may round to four decimal places below 0.0001. The internal value is exact.
Can I test Gemini against Claude or GPT?
Yes. Pick up to six models across providers in one run. Outputs stream in parallel, side by side.
Is my Google AI key sent to Freesuite?
No. freeprompttester.app is a static page. Your key goes only to Google's API in your browser. There is no Freesuite server.
Does freeprompttester.app support Gemini multimodal inputs?
Not in v1. Text-only prompts for now. Image and audio input support is on the roadmap.