---
name: argent-metro-debugger
description: Debug a JS runtime via CDP using argent debugger tools. Primary path is React Native via Metro (iOS / Android); a subset of the tools (debugger-connect, debugger-status, debugger-evaluate, debugger-log-registry) also drive a Chromium (CDP) app's renderer (an Electron app, or any Chromium browser exposing CDP) through the same surface. Use when connecting to the runtime, inspecting React components, reading console logs, or evaluating JavaScript.
---

## 1. Prerequisites

For **React Native (iOS / Android)**: requires **Metro dev server running** (default `localhost:8081`) and **a React Native app connected to Metro** (at least one CDP target). Verify via `debugger-status`.

For **Chromium (CDP)**: requires a Chromium/CDP app already available — an Electron app booted via `boot-device` with `electronAppPath`, or any Chromium browser exposing a CDP port (auto-discovered by `list-devices` on `9222` / `ARGENT_CHROMIUM_PORTS`). The debugger re-uses the page CDP session — `port` is ignored, `device_id` is the `chromium-cdp-<port>` value from `list-devices` / `boot-device`. Only `debugger-connect`, `debugger-status`, `debugger-evaluate`, `debugger-log-registry`, `view-network-logs`, and `view-network-request-details` work on Chromium (the latter two read the browser's native CDP Network recording for the active tab instead of the Metro-injected `fetch` interceptor); `debugger-component-tree`, `debugger-reload-metro`, `debugger-inspect-element`, and the `react-profiler-*` / `profiler-*` tools are RN-only and reject Chromium at the capability gate with `Tool 'X' is not supported on chromium app`.

### Android: reverse port for Metro

Android emulators and physical devices do not resolve the host's `localhost` by default. Before the RN app can reach Metro, forward port 8081 (or whichever port Metro is on) from the device back to the host:

```bash
adb -s <serial> reverse tcp:8081 tcp:8081
```

`<serial>` is the Android `serial` from `list-devices`. Once reversed, the app on the device connects to Metro just like an iOS simulator does, and all `debugger-*` / `network-*` / `react-profiler-*` tools work unchanged. If the device restarts or adb drops, re-run the command. A failing Metro connection on Android almost always means `adb reverse` has not been done or has been lost.

## 2. Tool Overview

All tools accept `port` (default 8081) AND `device_id` (the iOS Simulator UDID or Android serial, a.k.a. `logicalDeviceId` — the CDP-reported id that matches the device). Always make sure you target the correct app on the correct device.

One Metro port can serve multiple connected devices (e.g. two simulators on `localhost:8081`, or an iOS simulator alongside an Android emulator with `adb reverse` set up). `device_id` pins every debugger/network/profiler call to a specific device so sessions do not collide.

### Connect & diagnostics

| Tool               | Purpose                                                                                                                                                                                                                                                                                            |
| ------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `debugger-connect` | Connect to the JS runtime's CDP (Metro on iOS / Android; the page CDP session on Chromium). Returns port, projectRoot (empty on Chromium), deviceName, appName, `logicalDeviceId`, isNewDebugger, connected. The returned `logicalDeviceId` is the `device_id` for every subsequent debugger call. |
| `debugger-status`  | Like connect + loadedScripts, enabledDomains, sourceMapReady (no-op on Chromium). **Use to diagnose.**                                                                                                                                                                                             |

### Reload & recovery

| Tool                    | Purpose                                                                                       |
| ----------------------- | --------------------------------------------------------------------------------------------- |
| `debugger-reload-metro` | Reload all connected apps (like pressing "r" in Metro terminal). Needs a CDP target.          |
| `restart-app`           | Terminate and relaunch the app by device id and bundleId. Use when app lost Metro connection. |

### Inspection & console

| Tool                       | Purpose                                                                                                                                                                   |
| -------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `debugger-component-tree`  | Full React fiber tree (names, depth, bounding rects, tap coordinates).                                                                                                    |
| `debugger-inspect-element` | Inspect at (x, y) using **logical pixel coordinates** (not normalized 0-1): component hierarchy with source file:line and code fragment. See `references/source-maps.md`. |
| `debugger-log-registry`    | Get log summary (counts, clusters, file path). Then use `Grep`/`Read` on the flat log file for details.                                                                   |
| `debugger-evaluate`        | Run a JS expression in the app runtime.                                                                                                                                   |

---

## 3. Component Inspection

### `debugger-component-tree` vs `debugger-inspect-element`

|          | `debugger-component-tree`                                              | `debugger-inspect-element`                                      |
| -------- | ---------------------------------------------------------------------- | --------------------------------------------------------------- |
| Best for | Layout overview; finding tap targets; user-defined component hierarchy | Identifying a visible element and tracing it to its source file |
| Use when | "What's on screen and where?"                                          | "What component is this and where is it defined?"               |

Both can point to source files, but `inspect-element` is purpose-built for source tracing. `component-tree` is for orientation and tap-target discovery.

### `includeSkipped` guidance

Applies to both `debugger-component-tree` and `debugger-inspect-element`. Set to `true` only when debugging filter behavior — e.g., an expected component is missing from output, or you need to inspect a very specific branch of the tree (not just an overview).

> **Warning:** Output can be very large. Always combine with `maxNodes` (component-tree) or `maxItems` (inspect-element) and increase it incrementally (e.g., start at 50, then grow). Do not use `includeSkipped` without a limit on large apps.

---

## 4. Golden Rules

1. **`debugger-status` first when something fails** — it runs discovery, connection, and returns diagnostics.
2. **"No CDP targets" → get the app to connect to Metro** — use `restart-app` on the device, then retry `debugger-status`.
3. **Never assume one failure is permanent** — follow recovery steps before asking the user. For starting Metro and full failure recovery, see `argent-react-native-app-workflow` and `references/failure-scenarios.md`.

---

## 5. Reading Console Logs (Log Registry)

Logs are written to a flat log file on disk. Use the **log-registry → grep** pattern instead of reading logs inline.

### Workflow

1. **Call `debugger-log-registry`** — returns: `file` (log path), `totalEntries`, `byLevel`, `clusters` (top message groups with counts and source file info)
2. **Search the file** using `Grep` or `Read` with patterns from the response.

> **Large log files:** If `totalEntries` exceeds 10 000, delegate the grep exploration to an `Explore` subagent — pass it the file path, the entry format, and the patterns you need.

### Flat log format

One entry per line — fields (whitespace-separated, `|` delimiter before message)

| Field         | Example                     | Notes                                               |
| ------------- | --------------------------- | --------------------------------------------------- |
| `[L:<id>]`    | `[L:42]`                    | Unique grep anchor                                  |
| `<timestamp>` | `2026-03-17T14:30:00.000Z`  | ISO 8601                                            |
| `<LEVEL>`     | `ERROR`, `WARN `, `LOG  `   | Uppercase, padded to 5 chars                        |
| `<source>`    | `src/api/user.ts:42` or `-` | Relative path from source map; `-` if unavailable   |
| `<message>`   | `Failed login attempt`      | Full message; embedded newlines replaced with space |

Source attribution (file + line) is also available in `clusters` returned by `debugger-log-registry`.

Log files and messages can be large - **Always scope your search**, treat the file like a database, not a document.

When reading from the log file:

- Never `Read` the log file directly. Use `grep` or shell commands with limits using the above file format tips.
- Default to `-m 50` unless you need more.
- Use `tail -N` recent entries.
- `clusters[].message` gives you the exact text which you may look for

> **If the file is too large** Delegate to an `Explore` subagent with the file path, the format spec above, and the specific patterns you need.

---

## Quick Reference

| Action                            | Tool                                                                |
| --------------------------------- | ------------------------------------------------------------------- |
| Diagnose / check connection       | `debugger-status`                                                   |
| Connect to CDP (Metro / Chromium) | `debugger-connect`                                                  |
| Reload JS (already connected)     | `debugger-reload-metro`                                             |
| Relaunch app on device            | `restart-app`                                                       |
| Inspect component at point        | `debugger-inspect-element`                                          |
| Full component tree               | `debugger-component-tree`                                           |
| Console log overview              | `debugger-log-registry` (summary + log file path for `Grep`/`Read`) |
| Evaluate JS                       | `debugger-evaluate`                                                 |
