EidoStack

What is EidoStack?

EidoStack is a browser-based workspace for deciding which model to use. It is aimed at the evaluation step rather than production monitoring: run the same prompt against two models, read both answers next to each other, and see what each one cost.

How it works

Connect OpenAI, Anthropic or Google AI with your own API keys. Comparison mode sends one prompt to two selected models simultaneously and renders the responses side by side. Each response carries its token count and estimated cost, and a context view shows estimated tokens against the selected model's context window, with full, windowed or summarised context strategies.

System prompts are set per chat, so the effect of an instruction change can be observed directly. Chats are auto-named and organised in folders.

Key handling

Provider keys are encrypted in the browser under a master password and stored in browser storage; plaintext keys stay in memory only while a session is unlocked. Provider requests are issued from the browser with those credentials, so keys do not pass through EidoStack's servers. Encrypted vault backup and restore are supported.

Pricing

The free tier allows one configured provider, five chats and 50 messages per chat, with token, cost and context inspection, and comparison across those five chats. Pro lifts those limits to unlimited providers, chats and messages. Pro is $99/year billed annually, or $10 per month; the pricing page defaults to the annual figure and carries a monthly toggle. Prices read 8 September 2026.

Who it is for

Developers choosing between models for a specific application, particularly where the decision turns on cost and context consumption as much as answer quality. It is a manual side-by-side tool rather than an automated eval harness: there are no scored test suites or regression runs, so it complements rather than replaces a framework like Promptfoo or DeepEval.