Last updated 07-02-2026
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Prompto
Prompto is an open-source web application that gives you a polished interface for talking to large language models. It runs as a Progressive Web App in your browser, and your prompts route to whichever model provider you configure through LangChain.js.
The name blends "prompt" with the Italian word "pronto," meaning ready. You can switch between LangChain.js-supported LLMs and tune a temperature slider to control how creative or predictable replies feel. Chat keeps conversation context, Notebook sends one-off prompts without history, Templates store reusable prompts with dynamic placeholders, Arena lines up two models side by side, and Discussion spins up conversations between multiple AI personas.
The Prompto interface itself runs client-side. Settings, chat histories, templates, and configurations live in your browser's local storage, so nothing passes through a Prompto server. You bring your own API keys or point at a local Ollama instance.
Developers, tinkerers, and anyone who wants a self-hosted front end for multiple LLM backends without building one from scratch are the natural audience. The project is MIT licensed on GitHub.
Switch between LangChain.js-supported LLMs from one dashboard
Chat mode keeps full conversation context across a thread
Notebook fires isolated prompts with no prior context carried over
Save reusable prompt templates with dynamic contextual placeholders
Arena puts two LLM responses side by side for direct comparison
Discussion mode runs multi-turn conversations between AI personas
Temperature control on every mode to tune creativity vs predictability
Open source under the MIT License with full source on GitHub
Supports seven major LLM providers through LangChain.js in one interface
Five distinct interaction modes from single prompts to multi-model comparison
No Prompto account required; data stays in browser local storage
Installable as a PWA without a dedicated desktop application
You supply your own API keys and cover third-party LLM costs
Ollama requires separate CORS configuration when not running on localhost
Chat history and templates do not sync across devices because storage is local only
The hosted demo shows connection errors until you configure a provider in Settings
Is Prompto free to use?
Yes. Prompto is open source under the MIT License and the hosted demo is free to use. You only pay what your chosen LLM provider charges for API usage.
What LLM providers does Prompto support?
Prompto connects through LangChain.js to Ollama, OpenAI, Anthropic, Mistral, Cohere, Google, and xAI. Configure each provider with your API keys in the Settings page.
Does Prompto store my conversations on a server?
No. Prompto runs in your browser and stores settings, chat histories, templates, and configurations in local storage. You can delete all stored data from the Settings page at any time.
Can I use Prompto with a local Ollama model?
Yes. Ollama is the default provider in Settings. Enter your Ollama server URL and pick a model. CORS must be configured on the Ollama server if it runs on a different host than localhost.
Do I need to install anything to use Prompto?
Prompto works as a Progressive Web App in a modern browser. For local models, you run Ollama separately and point Prompto at your Ollama URL in Settings.
Is Prompto open source?
Yes. Prompto source code is on GitHub at github.com/antsanchez/prompto under the MIT License. You can self-host or contribute to the project.