Fixing a Claude Code PreToolUse Hook That Never Registered (RTK)

Symptom: an error under the success message

I had registered the RTK hook (rtk hook claude) under PreToolUse in ~/.claude/settings.json, but the Bash commands Claude ran were rarely rewritten to rtk. I’m on macOS with RTK installed through Homebrew (brew install rtk). I tried registering the global hook again.

$ rtk init -g
RTK hook registered (global).

  Command:   rtk hook claude
  RTK.md:    ~/.claude/RTK.md (10 lines)
  CLAUDE.md: @RTK.md reference added
rtk: Failed to parse ~/.claude/settings.json as JSON:
trailing comma at line 235 column 3

The first line of output looks like success, but a JSON parse error is printed right below it. And the ~/.claude/hooks folder had no files in it at all.

Cause: one comma

At first I suspected the plausible causes, one by one.

1. No bash on Windows. The old RTK hook (rtk-rewrite.sh) is a bash script, so on native Windows it doesn’t run and falls back to instructions in CLAUDE.md. This was macOS, so that wasn’t it.
2. PATH or jq. If the shell running the hook can’t find where rtk or jq is installed (/opt/homebrew/bin), the dependency check can fail silently. Plausible, but the logs said otherwise.

The real cause was a trailing comma on line 235 of ~/.claude/settings.json. Unlike JSONC, JSON fails to parse entirely if there’s a comma after the last item in an array or object.

"allow": [
  "Bash(npm run *)",
  "Bash(git commit *)",
  "Bash(git commit *)"
]

RTK reads the existing settings to merge in its PreToolUse entry, and that parse is where it failed. So “RTK hook registered” only meant the RTK.md and CLAUDE.md part succeeded. Nothing went into settings.json.

Why the hooks folder was empty

This was a separate source of confusion. Current RTK no longer creates a separate bash script (rtk-rewrite.sh). It registers the hook claude subcommand of the rtk binary directly in settings.json. An empty hooks folder looks wrong by the old behavior, but it’s normal for the current version.

Fix: remove the comma and register again

I made a backup, checked the lines around the problem, and removed the comma after the last item as shown above.

cp ~/.claude/settings.json ~/.claude/settings.json.bak
sed -n '225,240p' ~/.claude/settings.json

Then I validated the JSON and registered again. This time it finished without a parse error, and I confirmed the hook was in settings.json.

python3 -m json.tool < ~/.claude/settings.json > /dev/null && echo "OK"
rtk init -g
grep -A 3 "rtk hook claude" ~/.claude/settings.json

echo '{"tool_name":"Bash","tool_input":{"command":"git status"}}' | rtk hook claude

{"hookSpecificOutput":{"hookEventName":"PreToolUse",
"permissionDecisionReason":"RTK auto-rewrite",
"updatedInput":{"command":"rtk git status"},
"permissionDecision":"allow"}}

What I learned

• Read a tool’s success message to the end to see which step actually succeeded. Updating RTK.md and CLAUDE.md was not the same as registering the hook.
• settings.json is just a JSON file. One comma can silently break a tool’s whole write, so after editing by hand, validate it once with python3 -m json.tool.
• A tool’s internals change between versions (from a shell script to a binary subcommand). Feeding the hook input directly was faster and more reliable than leaning on old docs or guesses.
• Unlike single-value settings such as model or defaultMode, Claude Code hooks merge across user, project, and local scopes instead of overriding each other. Hooks for the same event in several scopes can all run, so check for leftover hooks from earlier attempts and keep them in one place.