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# Usage

Run `aider` with the source code files you want to edit.
These files will be "added to the chat session", so that
aider can see their
contents and edit them for you.

```
aider <file1> <file2> ...
```

## Adding files

Just add the files that the aider will need to *edit*.
If you add too many files, the LLM can get overwhelmed
and confused (and it costs more tokens).
Aider will automatically
pull in content from related files so that it can
[understand the rest of your code base](https://aider.chat/docs/repomap.html).

You can also run aider without naming any files and use the in-chat
`/add` command to add files.

Or you can skip adding files completely, and aider
will try to figure out which files need to be edited based
on your requests.

## LLMs

Aider uses GPT-4o by default, but you can
[connect to many different LLMs](/docs/llms.html).
Claude 3 Opus is another model which works very well with aider,
which you can use by running `aider --opus`.

You can run `aider --model XXX` to launch aider with
a specific model.
Or, during your chat you can switch models with the in-chat
`/model` command.

## Making changes

Ask aider to make changes to your code.
It will show you some diffs of the changes it is making to
complete you request.
It will git commit all the changes it makes,
so they are easy to track and undo.

You can always use the `/undo` command to undo changes you don't
like.