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Hooks

Hooks are shell commands DSCC runs around tool calls. Declare them in settings.hooks.PreToolUse[] and settings.hooks.PostToolUse[] (arrays of shell commands, config.rs:568–572).

Events

Defined at crates/runtime/src/hooks.rs:8–21.

Event Fires
PreToolUse Before a tool executes
PostToolUse After a tool returns

Stdin payload

Each hook receives JSON on stdin (hooks.rs:118–126):

{
  "hook_event_name": "PreToolUse",
  "tool_name": "bash",
  "tool_input": {...},
  "tool_input_json": "{...}",
  "tool_output": null,
  "tool_result_is_error": false
}

Environment variables

Set before the hook runs (hooks.rs:169–178):

Variable Present
HOOK_EVENT Always
HOOK_TOOL_NAME Always
HOOK_TOOL_INPUT Always (JSON)
HOOK_TOOL_IS_ERROR Always
HOOK_TOOL_OUTPUT PostToolUse only

Exit codes

From hooks.rs:164–213:

Exit Effect Stdout meaning
0 Allow Informational message
2 Deny Rejection reason
Other Warn, continue —
Signal Warn, continue —

Shell

OS Invocation
Unix /bin/sh -lc (hooks.rs:76–103)
Windows cmd /C (hooks.rs:76–103)

Example — reject rm -rf /

{
  "hooks": {
    "PreToolUse": [
      "if [ \"$HOOK_TOOL_NAME\" = \"bash\" ] && echo \"$HOOK_TOOL_INPUT\" | grep -q 'rm -rf /'; then echo 'refusing rm -rf /' >&2; exit 2; fi"
    ]
  }
}

See also