# What erlang_wasm is for

erlang_wasm runs WebAssembly inside your Erlang application, written in Erlang
itself: no native engine to build or ship. Read this page to decide whether it
fits what you want to do, and where to start if it does.

## What you can do with it

| use | what it looks like |
| --- | --- |
| portable plugins | add behaviour to a running system without loading native code into the VM |
| language runtimes | run JavaScript, Python or Lua that arrives at request time, one request per sandbox |
| rule evaluation | give rules explicit inputs, explicit permissions and a deadline |
| shared validators | run the same checks in several services and languages |
| small domain languages | compile a focused business language to WebAssembly and run it here |
| runtime research | inspect the whole machine in a high-level functional language |

## Is this the right runtime for you

Choose erlang_wasm when what must be true is about your application: request
lifetime and permissions are part of your product, you want to inspect or
change how the runtime behaves, a release that stays mostly Erlang makes
operations easier, and measured speed already meets your needs.

If the fastest possible guest execution is your main need, a native engine
such as Wasmtime, embedded through a NIF, fits better.

## Where to start

| I want to | start with |
| --- | --- |
| understand the words used everywhere else | [Concepts](concepts.md) |
| call exported WebAssembly functions from Erlang | [Getting started](getting-started.md), then [Call an export](examples/call-an-export.md) |
| run a program that has a `main` (a WASI command) | [Run a WASI command](examples/run-a-wasi-command.md) |
| run WebAssembly I did not write | [Stop a runaway](examples/stop-a-runaway.md), then [Workers](worker.md) |
| run JavaScript, Python or Lua source | [Run JavaScript](examples/run-javascript.md), [Run Python](examples/run-python.md), [Lua](lua.md) |
| stop paying interpreter startup on every request | [Restore a snapshot](examples/restore-a-snapshot.md) |
| speed up a workload I have measured | [Turn on the compiled tier](examples/turn-on-the-tier.md) |
| know what is installed and what I write | [What you get](what-you-get.md) |