> ## Documentation Index
> Fetch the complete documentation index at: https://mux.coder.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Customization

> Customize the compaction system prompt

You can customize how Mux summarizes conversations during compaction by overriding the `compact` agent.

## Override the `compact` agent

Create `.mux/agents/compact.md` in your project (or `~/.mux/agents/compact.md` for global):

```md theme={null}
---
name: Compact
base: compact
---

When summarizing:

- Preserve exact file paths and command output
- Prefer bullet lists over long prose
```

By default, your prompt is **appended** to the built-in `compact` agent.

### Replace instead of append

```md theme={null}
---
name: Compact
base: compact
prompt:
  append: false
---

Summarize in 5 bullets max. No preamble.
```

## Defaults (synced from source)

<Accordion title="Built-in compact agent system prompt">
  ```text theme={null}
  You are running a compaction/summarization pass. Your task is to write a concise summary of the conversation so far.

  IMPORTANT:

  - You have NO tools available. Do not attempt to call any tools or output JSON.
  - Simply write the summary as plain text prose.
  - Follow the user's instructions for what to include in the summary.
  ```
</Accordion>

<Accordion title="Default compaction instructions (user message)">
  ```text theme={null}
  Summarize this conversation for a new Assistant to continue helping the user.

  Your summary must be approximately 2000 words.

  Include:
  - The user's overall goal and current task
  - Key decisions made and their rationale
  - Current state of the work (what's done, what's in progress)
  - Important technical details (file paths, function names, configurations)
  - Any errors encountered and how they were resolved
  - Unresolved issues or blockers

  Do not include:
  - Suggestions for next steps
  - Conversational filler or pleasantries
  - Redundant information

  Write in a factual, dense style. Every sentence should convey essential context.
  ```
</Accordion>

## Notes

* Custom `compact` agents apply to both manual `/compact` and auto-compaction.
* Tools are always disabled during compaction.
* `-t` sets `maxOutputTokens`; Mux converts this into an approximate word target for the instruction message.