Crush Configuration

Crush uses JSON configuration files with the following priority (highest to lowest):

1. .crush.json (project-local, hidden)
2. crush.json (project-local)
3. $XDG_CONFIG_HOME/crush/crush.json or $HOME/.config/crush/crush.json (global)

Basic Structure

{
  "$schema": "https://charm.land/crush.json",
  "models": {},
  "providers": {},
  "mcp": {},
  "lsp": {},
  "hooks": {},
  "options": {},
  "permissions": {},
  "tools": {}
}

The $schema property enables IDE autocomplete but is optional.

Shell Expansion

Crush runs selected string fields through an embedded bash-compatible shell at load time, so values can pull from env vars, files, or helper commands.

Supported constructs (match the bash tool):

• $VAR and ${VAR}
• ${VAR:-default}, ${VAR:+alt}, ${VAR:?message}
• $(command) with full quoting and nesting
• Single- and double-quoted strings, escapes

Default semantics match bash: an unset variable expands to an empty string, no error. A failing $(command) is always a hard error. For required credentials, use ${VAR:?message} so a missing variable fails loudly at load time with your message.

{ "api_key": "${CODEBERG_TOKEN:?set CODEBERG_TOKEN}" }

Which fields expand

extra_body is a JSON passthrough. If you need env-driven values in a request body, put them in extra_headers, api_key, or base_url instead.

Empty-resolved headers are dropped

When a header value resolves to the empty string (unset variable, $(echo), or literal ""), the header is omitted from the outgoing request. This keeps optional env-gated headers like "OpenAI-Organization": "$OPENAI_ORG_ID" working cleanly when the var isn't set. Applies to MCP headers and provider extra_headers.

Security note

crush.json is trusted code. Any $(...) in it runs at load time with the invoking user's shell privileges, before the UI appears. Don't launch Crush in a directory whose crush.json you haven't reviewed.

Common Tasks

• Add a custom provider: add an entry under providers with type, base_url, api_key, and models.
• Disable a builtin or local skill: add the skill name to options.disabled_skills.
• Add an MCP server: add an entry under mcp with type and either command (stdio) or url (http/sse).

Model Selection

{
  "models": {
    "large": {
      "model": "claude-sonnet-4-20250514",
      "provider": "anthropic",
      "max_tokens": 16384
    },
    "small": {
      "model": "claude-haiku-4-20250514",
      "provider": "anthropic"
    }
  }
}

• large is the primary coding model; small is for summarization.
• Only model and provider are required.
• Optional tuning: reasoning_effort, think, max_tokens, temperature, top_p, top_k, frequency_penalty, presence_penalty, provider_options.

Custom Providers

{
  "providers": {
    "deepseek": {
      "type": "openai-compat",
      "base_url": "https://api.deepseek.com/v1",
      "api_key": "$DEEPSEEK_API_KEY",
      "models": [
        {
          "id": "deepseek-chat",
          "name": "Deepseek V3",
          "context_window": 64000
        }
      ]
    }
  }
}

• type (required): openai, openai-compat, or anthropic
• api_key, base_url, api_endpoint, and extra_headers are shell-expanded (see Shell Expansion).
• extra_body is a JSON passthrough and is not expanded.
• Additional fields: disable, system_prompt_prefix, extra_headers, extra_body, provider_options.

LSP Configuration

{
  "lsp": {
    "go": {
      "command": "gopls",
      "env": { "GOPATH": "$HOME/go" }
    },
    "typescript": {
      "command": "typescript-language-server",
      "args": ["--stdio"]
    }
  }
}

• command (required), args, env cover most setups.
• command, args, and env values are shell-expanded (see Shell Expansion).
• Additional fields: disabled, filetypes, root_markers, init_options, options, timeout.

MCP Servers

{
  "mcp": {
    "filesystem": {
      "type": "stdio",
      "command": "node",
      "args": ["/path/to/mcp-server.js"]
    },
    "github": {
      "type": "http",
      "url": "https://api.githubcopilot.com/mcp/",
      "headers": {
        "Authorization": "Bearer $GH_PAT"
      }
    }
  }
}

• type (required): stdio, sse, or http
• command, args, env, headers, and url are shell-expanded (see Shell Expansion).
• Additional fields: env, disabled, disabled_tools, timeout.

Options

{
  "options": {
    "skills_paths": ["./skills"],
    "disabled_tools": ["bash", "sourcegraph"],
    "disabled_skills": ["crush-config"],
    "tui": {
      "compact_mode": false,
      "diff_mode": "unified",
      "transparent": false
    },
    "auto_lsp": true,
    "debug": false,
    "debug_lsp": false,
    "attribution": {
      "trailer_style": "assisted-by",
      "generated_with": true
    }
  }
}

[!IMPORTANT] The following skill paths are loaded by default and DO NOT NEED to be added to skills_paths: .agents/skills, .crush/skills, .claude/skills, .cursor/skills

Other options: context_paths, progress, disable_notifications, disable_auto_summarize, disable_metrics, disable_provider_auto_update, disable_default_providers, data_directory, initialize_as.

Hooks

Hooks are user-defined shell commands that fire on agent events. Currently only PreToolUse is supported, which runs before a tool is executed.

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "^(edit|write|multiedit)$",
        "command": ".crush/hooks/protect-files.sh"
      },
      {
        "matcher": "^bash$",
        "command": ".crush/hooks/no-haskell.sh"
      }
    ]
  }
}

Hook Properties

• command (required): Shell command to execute. Runs via sh -c.
• matcher (optional): Regex pattern tested against the tool name. Empty or absent means match all tools.
• timeout (optional): Timeout in seconds. Defaults to 30.

Event Name Normalization

Event names are case-insensitive and accept snake_case variants: PreToolUse, pretooluse, pre_tool_use, and PRE_TOOL_USE all work.

How Hooks Work

1. When a tool is about to be called, all PreToolUse hooks with a matching matcher (or no matcher) run in parallel.
2. Duplicate commands are deduplicated — each unique command runs at most once.
3. The hook receives JSON on stdin and hook-specific environment variables.

Hook Input (stdin)

A JSON payload is piped to the hook command:

{
  "event": "PreToolUse",
  "session_id": "abc-123",
  "cwd": "/path/to/project",
  "tool_name": "bash",
  "tool_input": {"command": "ls -la"}
}

Hook Environment Variables

Hook Output

Exit code 0 — the hook succeeded. Stdout is parsed as JSON:

{"decision": "allow", "context": "optional context appended to tool result"}

• decision: allow to explicitly allow, deny to block, none (or omit) for no opinion.
• reason: Explanation text (used when denying).
• context: Extra context appended to the tool result.
• updated_input: Replacement JSON for the tool input. Last non-empty value wins.

Exit code 2 — the tool call is blocked. Stderr is used as the deny reason.

echo "No Haskell allowed" >&2
exit 2

Any other exit code — non-blocking error. The tool call proceeds as normal.

Claude Code Compatibility

Crush also supports the Claude Code hook output format:

{
  "hookSpecificOutput": {
    "permissionDecision": "allow",
    "permissionDecisionReason": "Auto-approved",
    "updatedInput": {"command": "echo rewritten"}
  }
}

Existing Claude Code hooks should work without modification.

Decision Aggregation

When multiple hooks match, their decisions are aggregated:

• Deny wins over allow — if any hook denies, the tool call is blocked.
• Allow wins over none — if no hook denies but at least one allows, the call proceeds.
• All deny reasons are concatenated (newline-separated).
• All context strings are concatenated (newline-separated).
• For updated_input, the last non-empty value wins.

Tool Permissions

{
  "permissions": {
    "allowed_tools": ["view", "ls", "grep", "edit"]
  }
}

Environment Variables

• CRUSH_GLOBAL_CONFIG - Override global config location
• CRUSH_GLOBAL_DATA - Override data directory location
• CRUSH_SKILLS_DIR - Override default skills directory