# Forge API levels

Every strategy and indicator file names the Forge API it was written for, on its first lines.

```python
FORGE_API = 1
```

## What the line does

The line is required and must be a whole number that Forge supports. Forge never reads a file as the oldest level when the line is missing. It refuses the file and says why:

- No line: `FORGE_API is missing: put FORGE_API = 1 on the first lines of the file`
- Not a whole number: `FORGE_API must be a whole number, got 'one'`
- A level Forge does not support: `FORGE_API = 7 is not supported; supported: 1`

## Supported levels

The latest level is Forge API 1. Supported levels: 1.

Each name in the reference says the level it appeared in, and a deprecated name says the level it was deprecated in.

## Older levels

Once Forge has more than one level, every docs and reference page shows a level switch. The docs of an older level stay readable under their own address, for example `/v/1/docs/get-started`, with a note that says which level you are reading and a link to the latest. Pages of an older level are not indexed by search engines.