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Legion is an Elixir runtime for AI agents that live inside your application and get things done by writing code.
In plain words
The easiest way to put AI agents inside your app.
An agent that actually does things
Instead of a chatbot that only talks, a Legion agent reaches into your application and acts: finds records, runs reports, changes settings, files the ticket. You decide which functions it may touch.
Chat is the least of it
The same agent can sit behind a chat window, power an MCP server for Claude or Cursor, or run as a background worker that clears a queue overnight. One runtime, many shapes.
Production essentials come in the box
Every action runs in a sandbox with time and memory limits, conversations are saved in your own database, and a dashboard shows exactly what the agent did and why. Nothing extra to buy or operate.
Features
Capable by default, contained by design.
F-01
Code instead of one-off tool calls
Agents can run vetted Lua (or Elixir) code that composes your tools to achieve things that were impossible before - with near zero configuration.
F-02
Sandboxed by default
Every evaluation runs in a monitored process with timeout, memory, and CPU budgets. Lua can't reach the host BEAM at all - the only way out is the tools you registered.
F-03
Tools are plain modules
use Legion.Tool on any module and the agent reads its source and calls its functions directly. Nothing to define, nothing to keep in sync as your app changes.
F-04
Scoped to the signed-in user
Set auth context before the agent starts and read it inside your tools at runtime. Every call the agent makes is scoped to that user, and the generated code never sees the credentials.
F-05
Agents are BEAM processes
Start one, keep it around, message it like a GenServer. Supervision trees, pools, and agents that delegate to other agents all work the way you expect.
F-06
Backed by your Postgres
Point Legion at your Repo and you'll have persistence and rate limiting for your agents.
F-07
Observability is included
Telemetry events at every level - agent, message, iteration, LLM call, sandbox eval - and the legion_web LiveView dashboard shows live conversations and every line of code an agent writes.
We are Software Mansion
You might know us from Elixir Stream Week, Global Elixir Meetups, or from projects like Popcorn and Membrane. But that’s not all we do.
We help teams build exceptional software - from developer tools to production-ready applications. Let’s talk about how we can support your next project.