node inspect path/to/script.js

The `debug>` prompt accepts:

| Command | Action |
|---|---|
| `c` or `cont` | continue |
| `n` or `next` | step over |
| `s` or `step` | step into |
| `o` or `out` | step out |
| `pause` | pause running code |
| `sb('file.js', 42)` | set breakpoint at file.js line 42 |
| `sb(42)` | set breakpoint at line 42 of current file |
| `sb('functionName')` | break when function is called |
| `cb('file.js', 42)` | clear breakpoint |
| `breakpoints` | list all breakpoints |
| `bt` | backtrace (call stack) |
| `list(5)` | show 5 lines of source around current position |
| `watch('expr')` | evaluate expr on every pause |
| `watchers` | show watched expressions |
| `repl` | drop into REPL in current scope (Ctrl+C to exit REPL) |
| `exec expr` | evaluate expression once |
| `restart` | restart script |
| `kill` | kill the script |
| `.exit` | quit debugger |

**In the `repl` sub-mode:** type any JS expression, including access to locals/closure variables. `Ctrl+C` exits back to `debug>`.

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To start a process with the inspector from the beginning:

```bash
node --inspect script.js           # listen on 127.0.0.1:9229, keep running
node --inspect-brk script.js       # listen AND pause on first line
node --inspect=0.0.0.0:9230 script.js   # custom host:port

node --inspect-brk --import tsx script.ts

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npm i -g chrome-remote-interface        # or project-local

Driver script (save as `/tmp/cdp-debug.js`):

```javascript
const CDP = require('chrome-remote-interface');

(async () => {
  const client = await CDP({ port: 9229 });
  const { Debugger, Runtime } = client;

  Debugger.paused(async ({ callFrames, reason }) => {
    const top = callFrames[0];
    console.log(`PAUSED: ${reason} @ ${top.url}:${top.location.lineNumber + 1}`);

    // Walk scopes for locals
    for (const scope of top.scopeChain) {
      if (scope.type === 'local' || scope.type === 'closure') {
        const { result } = await Runtime.getProperties({
          objectId: scope.object.objectId,
          ownProperties: true,
        });
        for (const p of result) {
          console.log(`  ${scope.type}.${p.name} =`, p.value?.value ?? p.value?.description);
        }
      }
    }

    // Evaluate an expression in the paused frame
    const { result } = await Debugger.evaluateOnCallFrame({
      callFrameId: top.callFrameId,
      expression: 'typeof state !== "undefined" ? JSON.stringify(state) : "n/a"',
    });
    console.log('state =', result.value ?? result.description);

    await Debugger.resume();
  });

  await Runtime.enable();
  await Debugger.enable();

  // Set a breakpoint by URL regex + line
  await Debugger.setBreakpointByUrl({
    urlRegex: '.*app\\.tsx$',
    lineNumber: 119,       // 0-indexed
    columnNumber: 0,
  });

  await Runtime.runIfWaitingForDebugger();
})();

node /tmp/cdp-debug.js

mkdir -p /tmp/cdp-tools && cd /tmp/cdp-tools && npm i chrome-remote-interface
NODE_PATH=/tmp/cdp-tools/node_modules node /tmp/cdp-debug.js

cd /home/bb/hermes-agent/ui-tui
npm run build    # produce dist/ once so transpile isn't needed on first load
node --inspect-brk dist/entry.js

Then inside `debug>`:

When it pauses, `repl` → inspect `props`, state refs, `useInput` handler values, etc.

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Interacting with the TUI (typing in its window) continues to advance execution; your debugger can pause it on a breakpoint at any `sb(...)`.

cd /home/bb/hermes-agent/ui-tui

In another terminal: `node inspect -p <pid>`, then `sb('src/app/foo.tsx', 42)`, `cont`.

Use `--no-file-parallelism` (vitest) or `--runInBand` (jest) so only one worker exists — debugging a pool is painful.

// CPU profile for 5 seconds
await client.Profiler.enable();
await client.Profiler.start();
await new Promise(r => setTimeout(r, 5000));
const { profile } = await client.Profiler.stop();
require('fs').writeFileSync('/tmp/cpu.cpuprofile', JSON.stringify(profile));
// Open /tmp/cpu.cpuprofile in Chrome DevTools → Performance tab

// Heap snapshot
await client.HeapProfiler.enable();
const chunks = [];
client.HeapProfiler.addHeapSnapshotChunk(({ chunk }) => chunks.push(chunk));
await client.HeapProfiler.takeHeapSnapshot({ reportProgress: false });
require('fs').writeFileSync('/tmp/heap.heapsnapshot', chunks.join(''));

node --inspect-brk script.js &
node inspect -p $!

**"What's the call path into this function?"**

**"This async chain hangs — where?"**

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