rewatch

A smarter cargo-watch alternative, designed for AI coding agents.

The problem with cargo-watch

Tools like cargo-watch rebuild on every file save. When an AI agent (Claude Code, Cursor, Copilot) edits multiple files in rapid succession, this triggers dozens of redundant builds — wasting CPU and producing noise.

rewatch takes a different approach:

1. Detects file changes and kills the running process
2. Waits for Enter (or a trigger file) before restarting — so the agent can finish all its edits first
3. Restarts once, when you're actually ready

This means one clean build instead of twenty failed ones.

Install

cargo install rewatch

Quick start

# CLI arguments
rewatch -w src,Cargo.toml -e rs,toml -- cargo run

# Or with a config file (just run `rewatch` with no arguments)
rewatch

Config file

Create rewatch.toml in your project root:

command = "cargo run"
watch = ["src", "Cargo.toml"]
ext = ["rs", "toml"]

[env]
RUST_LOG = "debug"

CLI arguments override config file values.

Using with AI coding agents

The trigger file feature enables a fully automated edit-build-test loop:

1. Run rewatch in one terminal
2. The AI agent edits your code — rewatch detects changes and kills the running process
3. When the agent is done, it touches the trigger file — rewatch restarts immediately (no Enter needed)
4. The agent sees build output and iterates

Setup with Claude Code

rewatch.toml:

command = "cargo run"
watch = ["src"]
ext = ["rs", "toml"]
trigger = ".rewatch-trigger"

CLAUDE.md:

After making code changes that require a rebuild, run: touch .rewatch-trigger

.gitignore:

.rewatch-trigger

Run rewatch in one terminal and Claude Code in another — they work together automatically.

How it works

1. Starts your command
2. Watches files for changes (event-driven, not polling)
3. On change — kills the process (entire tree) and shows diff-style indicators:
   • + created, ~ modified, - removed
   • Duplicate file names are suppressed — each file shown only once
4. Waits for Enter before restarting (so you or the agent can finish edits)
5. On process crash — shows exit code, waits for Enter
6. On trigger file — restarts immediately without Enter (stale trigger files are cleaned up on startup)
7. Hot-reloads its own config: editing rewatch.toml (or the file passed via --config) re-reads the config and respawns the child with the new command/env/watch paths. No-op saves (touch, :w without edits) are skipped via content-hash dedup.
8. Ctrl+C — first press kills the child process and waits, second press exits rewatch

Note: By default, the trigger file only works when rewatch is waiting for Enter (after file changes or process exit). Use trigger_always = true or -T to allow trigger to restart even without file changes.

CLI options

Option	Description
-w, --watch <paths>	Paths to watch, comma-separated or multiple flags
-e, --ext <extensions>	Filter by extensions (.rs and rs both work). Only applies to files inside watched directories — files listed explicitly in -w always trigger.
-t, --trigger <path>	Trigger file for auto-restart
-T, --trigger-always	Trigger restarts even without file changes
-E, --env <KEY=VALUE>	Set environment variables (overrides TOML [env])
-c, --config <path>	Use a custom config file instead of rewatch.toml. The file is required when this flag is given.
-- <command...>	Command to run

Example with env override:

rewatch -E SQLX_MIGRATE_IGNORE_MISSING=true

Config file reference

command = "cargo run --release"     # command to execute (shell-style quoting supported)
watch = ["src", "Cargo.toml", ".env"] # files/directories to watch
ext = ["rs", "toml"]                # filter by extension (optional, applies to dirs only)
trigger = ".rewatch-trigger"        # trigger file (optional)
trigger_always = false              # trigger restarts even without file changes (default: false)

[env]                               # environment variables for the child process
RUST_LOG = "debug"
SQLX_MIGRATE_IGNORE_MISSING = "true"

Platform support

• Windows: kills process tree via Win32 Job Objects
• Linux: kills process group via kill(-pgid, SIGTERM)
• macOS: same as Linux

Powered by notify (OS-native file system events) and process-wrap (from the watchexec project).

rewatch vs cargo-watch

	cargo-watch	rewatch
Rebuilds on every save	Yes	No — waits for Enter or trigger
AI agent friendly	No — floods with builds	Yes — trigger file for automation
Kills process tree	Partial	Full (Job Objects / process groups)
Config file	No	rewatch.toml
Language-agnostic	Cargo only	Any command

License

MIT