Free LLM Prompt Playground — One Prompt, Any Model, In Your Browser

freeprompttester.app is a free, browser-based LLM prompt playground that supports more providers than any single-vendor playground. Bring your own API keys, write a prompt, pick from 25+ models across Anthropic, Google, xAI, Mistral, DeepSeek, Groq, Cohere and OpenRouter (for OpenAI's GPT family), and run them in parallel with streamed output, latency, token usage and per-call cost displayed live. The whole thing is a static HTML page — no proxy, no sign-up, no Freesuite servers in the request path.

What is an LLM prompt playground?

An LLM playground is an interactive UI for testing prompts against language models without writing any code. You type a prompt, click run, and read the response. Most playgrounds (OpenAI's, Anthropic's Workbench, Google AI Studio, xAI's console) are tied to one vendor — useful for that vendor's models, useless for cross-provider comparison. freeprompttester.app is provider-agnostic.

Use cases

• Picking a model for a new project. Run your representative prompts against your shortlist, compare quality and cost, decide.
• Prompt engineering. Iterate on a prompt across multiple models so you don't accidentally optimize for one provider's quirks.
• Cost benchmarking. Multiply per-call cost by your expected volume to see real monthly spend before committing.
• Vendor swap evaluation. Already on OpenAI? Run your top prompts against Claude or Gemini to see if a switch is worth it.
• Quick sanity check. When a model behaves oddly in production, paste the prompt into freeprompttester.app and try a few alternatives.

How freeprompttester.app works

You paste API keys into the keys panel — one per provider, stored in your browser's localStorage. You write a system prompt (optional) and a user prompt. You select up to six models. You click Run. freeprompttester.app fires parallel fetch() calls directly from your browser to each provider's chat completion endpoint, parses the streamed SSE response, and renders tokens into per-model cards as they arrive. When the response finishes, the provider returns input and output token counts; freeprompttester.app multiplies those by the published per-million rates and shows the exact cost of each call.

Two modes: single-shot and chat

freeprompttester.app supports two playgrounds in one page. Single-shot mode is the default — one prompt, up to 6 models, parallel responses. Chat mode (top-tab toggle) holds a parallel multi-turn conversation with up to 3 models simultaneously, each with its own history. Same shared input bar, broadcasts every message to every column, watch each model's thread evolve independently. Useful for testing system prompts, persona stickiness, and how models handle multi-turn instruction following. State is kept separate between modes so your single-shot prompt and your chat history never bleed into each other.

✦ Synthesize multi-model responses

After a single-shot run completes with at least two models, the ✦ Synthesize button in the run bar lights up. Click it to send all completed responses to a chosen model that produces a combined answer with explicit consensus and disagreement sections. The synthesis card renders full-width at the top of the results grid with a gold border. Default synthesis instruction is editable. This is the part of an LLM playground that no other tool ships — it turns "I have N opinions" into "I have one decision-ready answer with uncertainty marked."

Models in the picker

Anthropic Claude Opus 4.7, Sonnet 4.6, Haiku 4.5. Google Gemini 2.5 Pro, 2.5 Flash, 2.0 Flash. xAI Grok 4, Grok 4 Fast, Grok 3. Mistral Large 2, Medium 3, Small 3.1. DeepSeek V3.1, R1. Groq-hosted Llama 4 Scout 17B, Llama 3.3 70B, Llama 3.1 8B. Cohere Command A, Command R+, Command R. Via OpenRouter, the entire live catalog of 370+ models is loaded automatically — GPT-5, GPT-5 mini, GPT-4.1, o4-mini, plus every Anthropic, Google, Meta, Qwen, Mistral, DeepSeek, xAI, Cohere, Perplexity, NVIDIA, MiniMax model OpenRouter exposes. The OpenRouter tab includes a provider sub-filter dropdown and a search box to find any specific model by name or id.

Privacy

freeprompttester.app is a static HTML/CSS/JS bundle. The only network requests it makes are to AI providers, using keys you paste. There is no Freesuite backend, no logging, no third-party analytics on input. Verify by inspecting the Network tab while running a prompt.

Frequently Asked Questions

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