Checkfu documentation

Run durable agents with the harness and model you choose.

Checkfu runs durable agents without locking you to one agent loop or model. Define an Agent once and start Sessions through one API. New Sessions can adopt a different harness or model without changing the durable Session, event, tool, or permission contracts around them.

Run your first Session

Create and publish an Agent, send a message, and follow its event stream.

Core concepts

Concept	Meaning
Agent	The instructions, tools, and execution stack you publish.
Execution stack	A HarnessProfile runs the loop, a ModelRoutingProfile routes model calls, and a SandboxProfile defines the sandbox configuration.
Session	A durable conversation that survives individual Runs and process restarts.
Events	The ordered record of messages, tool calls, status changes, and usage inside a Session.

The extra execution-stack choices are what make Checkfu harness-neutral. Most applications select existing Workspace names when they create an Agent; they do not configure the stack on every Session.

How it works

1. Create and publish an Agent

   Choose its instructions, tools, HarnessProfile, ModelRoutingProfile, and SandboxProfile.

2. Start a Session

   A Session admits one immutable Agent version and acts as one Principal.

3. Send events

   Append a message, then follow the same ordered log through execution and settlement.

const session = await checkfu.sessions.create({
  agent: "agent_…",
  principal: "prin_…",
})

await checkfu.sessions.events.send(session.id, {
  type: "user.message",
  payload: {
    content: "Summarize this repository.",
    authored_by: "prin_…",
    caused_by: { kind: "api" },
  },
})

const turnBoundaries = new Set([
  "session.status_idle",
  "session.status_completed",
  "session.status_failed",
  "session.status_canceled",
])

for await (const event of checkfu.sessions.events.stream(session.id)) {
  if (turnBoundaries.has(event.type)) break
}

Explore by task

Agents

Define behavior, publish immutable versions, and choose an execution stack.

Sessions

Drive durable conversations and read settlement from the event log.

Tools

Use harness tools, connected provider tools, or tools served by your app.

Bring a harness

Run Claude Agent, Codex, pi, or your own ACP-compatible loop behind the same API.

Plain HTTP is the public contract. The TypeScript SDK and CLI provide convenient clients for the same API. If the main quickstart does not fit your setup, choose another starting path.