Instruction Files

Overview

mux layers instructions from two locations:

1. ~/.mux/AGENTS.md (+ optional AGENTS.local.md) — global defaults
2. <workspace>/AGENTS.md (+ optional AGENTS.local.md) — workspace-specific context

Priority within each location: AGENTS.md → AGENT.md → CLAUDE.md (first match wins). If the base file is found, mux also appends AGENTS.local.md from the same directory when present.

Note: mux strips HTML-style markdown comments (<!-- ... -->) from instruction files before sending them to the model. Use these comments for editor-only metadata—they will not reach the agent.

Scoped Instructions

mux supports Scoped Instructions that activate only in specific contexts. You define them using special headings in your instruction files:

• Mode: <mode> — Active only in specific interaction modes (e.g., plan, exec).
• Model: <regex> — Active only for specific models (e.g., GPT-4, Claude).
• Tool: <tool_name> — Appended to the description of specific tools.

General Rules

• Precedence: Workspace instructions (<workspace>/AGENTS.md) are checked first, then global instructions (~/.mux/AGENTS.md).
• First Match Wins: Only the first matching section found is used. Overriding global defaults is as simple as defining the same section in your workspace.
• Isolation: These sections are stripped from the general <custom-instructions> block. Their content is injected only where it belongs (e.g., into a specific tool's description or a special XML tag).
• Boundaries: A section's content includes everything until the next heading of the same or higher level.

Mode Prompts

Use mode-specific sections to optimize context and customize behavior for specific workflow stages. The active mode's content is injected via a <mode> tag.

Syntax: Mode: <mode> (case-insensitive)

Example:

# General Instructions

- Be concise

## Mode: Plan

When planning:

- Focus on goals and trade-offs
- Propose alternatives with pros/cons

## Mode: Compact

- Preserve key decisions
- Be extremely concise

Available modes:

• exec (default) — Normal operations.
• plan — Active in Plan Mode.
• compact — Used during /compact to guide history summarization.

Model Prompts

Scope instructions to specific models or families using regex matching. The matched content is injected via a <model-...> tag.

Syntax: Model: <regex>

• Regexes are case-insensitive by default.
• Use /pattern/flags for custom flags (e.g., /openai:.*codex/i).

Example:

## Model: sonnet

Be terse and to the point.

## Model: openai:.\*codex

Use status reporting tools every few minutes.

Tool Prompts

Customize how the AI uses specific tools by appending instructions to their descriptions.

Syntax: Tool: <tool_name>

• Tool names must match exactly (case-insensitive).
• Only tools available for the active model are augmented.

Example:

## Tool: bash

- Use `rg` instead of `grep` for file searching

## Tool: file_edit_replace_string

- Run `prettier --write` after editing files

# Tool: status_set

- Set status url to the Pull Request once opened

Available tools: bash, file_read, file_edit_replace_string, file_edit_insert, propose_plan, todo_write, todo_read, status_set, web_search.

Practical layout

~/.mux/
  AGENTS.md          # Global instructions
  AGENTS.local.md    # Personal tweaks (gitignored)

my-project/
  AGENTS.md          # Project instructions (may include "Mode: Plan", etc.)
  AGENTS.local.md    # Personal tweaks (gitignored)