Author prompts. Fan them out to Claude, GPT, Gemini, OpenRouter, Groq, Ollama, LM Studio, and local WebGPU models side-by-side. See streamed outputs with latency and cost. Keys never leave your browser.

Single HTML file. No server. No build step. Open index.html or visit the hosted version.

Live · part of the NakliTechie browser-native series.

• Prompt Studio — paste a prompt with optional {{variables}}, pick providers, click Run, watch side-by-side streamed outputs with latency and cost-per-call.
• Models & Keys — per-provider key fields, "test" button against each provider's models endpoint, model matrix with pricing, rate-limit calculator.
• Run history — every run saved to OPFS, replay or fork from the History tab, export the whole archive to a folder via the File System API.
• Local WebGPU models — Gemma 3 1B, Qwen 2.5 0.5B, SmolLM2 1.7B running entirely in-browser via Transformers.js, compared head-to-head with frontier API models in the same fan-out.
• JS API — opt-in window.mantra surface (runPrompt, getRuns, onRun) plus cross-tab postMessage so other browser-native apps can push prompts into Mantra.

• Wave 2 — Eval Bench: datasets, assertions (exact / regex / JSON-schema / LLM-as-judge), pairwise compare, regression dashboards.
• Wave 3 — RAG Lab: chunker preview, embedding playground, retriever simulator, grounding checker, vector store browser.

Stateless calculators that pair with this workbench (token counter, cost estimator, jailbreak / injection / PII scanner) live in BOFH.

• API keys live in your browser's localStorage. No telemetry, no key relay.
• Prompts are sent directly from your browser to whichever provider you select. Mantra has no server in the middle.
• Run history lives in your browser's OPFS by default (private to this origin). Export to a folder you control via the History tab.

cd Mantra
python3 -m http.server 8080
# open http://localhost:8080

Or just open index.html in a modern browser. Anthropic / OpenAI / Gemini direct browser calls require recent browser versions; the Anthropic adapter sends anthropic-dangerous-direct-browser-access: true.

Edit the PROVIDERS constant in index.html. Shape required:

{
  id: 'myprov',
  label: 'My Provider',
  baseUrl: 'https://...',
  keyHeader: 'Authorization', keyPrefix: 'Bearer ',
  modelsUrl: 'https://.../v1/models',  // optional, for Test
  defaultModel: '...',
  knownModels: ['...'],
  shape: 'openai',  // or 'anthropic' / 'gemini'
}

If the provider speaks OpenAI's chat-completions schema (most do), shape: 'openai' works out of the box. Anthropic and Gemini have their own SSE shapes — see the parseSSE* functions.

This project follows the NakliTechie single-file pattern — markup, styles, and logic in one HTML file. The CDN imports for Transformers.js use @4/+esm exactly (older versions crash with newer models). Workers are created via blob URLs with type: 'module'.

MIT.