FlowKoi runs your pre-configured flows — a CLAUDE.md + tools + .claude/ skills + optional env — inside ephemeral containers. The Sandcastle API ships that capability as a REST surface so your servers can:
- Trigger a run with a prompt and any input files you want injected.
- Stream output as the agent works (SSE or WebSocket).
- Send follow-up messages mid-run, inject more files, stop early.
- Receive a signed webhook the moment a run finishes.
If you’ve used Anthropic Managed Agents, E2B, or Modal sandboxes, this lives in the same category — with one knob: you ship the agent’s brain (CLAUDE.md + skills) once in the dashboard, then trigger it as many times as you need from the API.
Where to start
Quickstart
Make your first API call in 5 minutes —
curl, Node, Python.Authentication
Mint a project API key and use it from your server.
TypeScript SDK
npm install @flowkoi/sdk and skip the wire-format details.API reference
Every endpoint, every field. Generated from our OpenAPI spec.
The mental model
- Flow — the recipe. Lives in your project, version-controlled. Defines what the agent knows and which tools it has.
- Run — one execution of a flow inside a fresh container. Has a
runId, a streaming surface, and a terminal state. - API key — project-scoped credential. Mint as many as you want, revoke any time.
- Webhook — outbound HMAC-signed POST to your URL when a run finishes.
Everything else — rate limits, idempotency, file injection, mid-run messages — is plumbing around those four nouns.