---
title: "Missions and runs"
description: "Separate the declared definition of work from each execution."
order: 4
---

# Missions and runs

A **mission** declares goals, constraints, inputs, and the steps and checks needed to finish. A **run** is one execution pinned to an immutable mission revision.

```kdl
version 2
mission "example/first-note" state="ready" {
  goal "A short project introduction exists in WELCOME.md."
  step "write" timeout="15m" {
    assigned-to "agent/example/worker"
    goal "WELCOME.md contains the project introduction."
  }
}
```

## Publish, then start

`fractal apply mission.kdl --as person/ada` saves the definition. It does not start work. `fractal missions start` creates a run with its own identity, workspace, and history. Read [Your first mission](../getting-started/first-mission.md) for the full procedure.

Give goals observable end states. Keep operational instructions in constraints or documents named by the mission. A mission should say what must be true, not merely that an agent should try.

## Revising a running mission

Publishing a new definition does not silently change existing runs. An explicit run revision creates a new generation with preserved history. Finished work carries forward only where it remains compatible with the new plan; changed work and its dependents may need to run again.

## Finite and continuing work

A finite mission ends when its work and checks finish. For continuing event intake, use a deliberate retirement gate to keep subscriptions alive until you choose to stop them. Do not create an empty mission to keep an agent available: declare an independent agent instead.

See [Missions in practice](../guides/missions-in-practice.md) for dependencies, review, revisions, and queued runs.