> ## Documentation Index > Fetch the complete documentation index at: https://docs.twinbay.ai/llms.txt > Use this file to discover all available pages before exploring further. # Introduction > Private, stateful copies of the APIs your agent calls Twinbay gives every test run its own copy of the third-party APIs your code calls. You describe the state you need in plain language, Twinbay hands back a private hostname and a provider-shaped API key, and the vendor's own SDK talks to it without a code change beyond the base URL. A twin is not a schema-generated mock. Each one is written by hand against a provider's behavior: its state machines, pagination, idempotency, authentication and error envelopes. CI validates every twin by running the provider's official SDK against it. ## What you get Hard bounces, declined sends, revoked keys, half-finished workflows. Ask for it in one sentence. Every sandbox has its own hostname, records, credentials and request log. Run CI jobs in parallel without sharing state. Ask for a sandbox and Twinbay builds it: a container per twin, seeded from your scenario, serving within a couple of minutes. Stop it when the suite ends. Read back every request: method, path, body, status and latency. ## Where to go next From an API key to a passing SDK call against a seeded sandbox. Twins, sandboxes, scenarios, credentials, records and time. Provision and inspect sandboxes from a shell or a CI job. Give a coding agent the same operations as tools. Twinbay is free for academic researchers. [Sign up in the console](https://console.twinbay.ai) with an email address.