fdb 1.5.1

Flutter Debug Bridge - CLI for AI agents to interact with running Flutter apps on device. Launch, reload, screenshot, inspect widget tree, filter logs.

Give your AI agent eyes and hands on your Flutter app.

fdb is a CLI that lets AI coding agents launch, hot reload, screenshot, inspect, and kill Flutter apps running on real devices and simulators -- all from the terminal, no IDE required.

Claude Code  ·  OpenCode  ·  Cursor  ·  any agent that can run bash

Why fdb?

AI agents are great at writing Flutter code. But they can't see what the app looks like, read runtime logs, or inspect the widget tree.

fdb fixes that:

• Launch a Flutter app on any connected device or simulator
• Hot reload / restart after code changes
• Screenshot so the agent can see the UI
• Read logs filtered by tag
• Inspect the widget tree
• Select widgets by tapping on device

Zero dependencies. Pure Dart. Works on macOS and Linux.

Why not the official Flutter MCP server?

The Dart & Flutter MCP server handles code analysis, pub.dev search, formatting, and can also introspect a running app via the Flutter inspector. fdb does something different: runs the app on a real device and lets the agent interact with it via a bash-native CLI — no MCP client required.

	fdb	Flutter MCP server
Architecture	CLI -- plain bash commands	MCP protocol -- requires a compatible client
Context cost	Minimal. Agent runs a command, gets text output.	MCP tool schemas and responses are injected into context on every call, eating tokens even when unused.
Works with	Any agent that can run bash (Claude Code, OpenCode, Cursor, custom scripts, CI)	Only MCP-compatible clients
Progressive disclosure	Ships a skill file — agent loads best practices on demand, not upfront	All tools exposed at once
Device interaction	Launch, hot reload, screenshot, logs, widget tree, tap, input, scroll, swipe, back, deeplink, SharedPreferences, clean	Widget tree inspection and runtime errors via Flutter inspector (read-only)
Setup	dart pub global activate -- done	Per-client MCP config (JSON, YAML, or GUI depending on client)

tl;dr: Use the Flutter MCP server for code analysis and package management. Use fdb when your agent needs to run the app, see it, and interact with it.

Install

Using an AI agent? Just tell it:

Fetch and follow instructions from https://raw.githubusercontent.com/andrzejchm/fdb/main/doc/README.agents.md

Or install manually:

dart pub global activate fdb

Requires Dart SDK >= 3.0.0. Make sure ~/.pub-cache/bin is in your PATH.

Or from git (latest main):

dart pub global activate --source git https://github.com/andrzejchm/fdb.git

Quick Start

# Launch your app on a connected device
fdb launch --device <device_id> --project /path/to/your/flutter/app

# See what it looks like
fdb screenshot

# Make a code change, then hot reload
fdb reload

# Check the widget hierarchy
fdb tree --depth 5 --user-only

# Read filtered logs
fdb logs --tag "MyFeature" --last 30

# Done? Kill the app
fdb kill

Commands

Device & app lifecycle

Command	Description
fdb devices	List connected devices
fdb launch --device <id> --project <path> [--verbose]	Launch app, wait for start; emits LAUNCH_ERROR= / LAUNCH_ERROR_CAUSE= / HINT: on stderr for failures
fdb reload	Hot reload
fdb restart	Hot restart
fdb doctor	Pre-flight check for app, VM service, fdb_helper, platform tools, and device state
fdb status	Check if app is running
fdb kill	Stop app, clean up

Visual inspection

Command	Description
fdb screenshot [--output <path>] [--full]	Screenshot (all platforms; --full skips downscaling)
fdb logs --tag <tag> --last <n>	Filtered logs
fdb syslog [--since <dur>] [--predicate <str>] [--last <n>] [--follow]	Native system logs (Android logcat, iOS syslog, macOS log)
fdb crash-report [--app-id <id>] [--last <dur>] [--all]	Fetch the most recent OS-level crash record (jetsam, LMK, native crashes)
fdb tree --depth <n> [--user-only]	Widget tree
fdb describe	Compact screen snapshot: interactive elements + visible text (requires fdb_helper)
fdb select on/off	Widget selection mode
fdb selected	Get selected widget info

Interaction (requires fdb_helper)

Command	Description
fdb double-tap --text/--key/--type <selector> [--index N] | --x X --y Y | --at X,Y	Double-tap a widget or screen coordinates
fdb native-tap --at x,y	Tap native (non-Flutter) UI — system dialogs, permission sheets (Android: adb shell input tap; iOS sim: falls back to in-process tap with a warning). Physical iOS and macOS not supported — use fdb tap --at instead.
fdb tap --text/--key/--type <selector>, --at x,y, or @N	Tap a widget, coordinates, or describe ref
fdb longpress --text/--key/--type <selector> [--duration <ms>] or --at x,y	Long-press a widget or coordinates
fdb input [--text/--key/--type <selector>] <text>	Enter text into a field
fdb scroll <direction> [--at x,y] [--distance px]	Scroll in a direction
fdb scroll --from x,y --to x,y	Drag gesture between two points
fdb scroll-to --text/--key/--type <selector> [--index N]	Scroll until widget is visible
fdb wait --key/--text/--type/--route <selector> --present|--absent [--timeout <ms>]	Wait for a widget or route condition without shell polling
fdb swipe <direction> [--key/--text/--type <selector>]	Swipe widget (PageView, Dismissible)
fdb back	Navigate back (Navigator.maybePop)
fdb deeplink <url>	Open a deep link

Data & state (requires fdb_helper)

Command	Description
fdb shared-prefs get|get-all|set|remove|clear	Read/write SharedPreferences
fdb clean	Clear app cache and data directories

VM service extensions

Command	Description
fdb ext list	List all registered ext.* VM service extensions across isolates, sorted and deduplicated
fdb ext call <method> [--arg key=value ...]	Invoke a VM service extension and print the JSON result

# Discover what debug hooks are registered in the running app
fdb ext list
# ext.dart.io.getOpenFiles
# ext.flutter.debugPaint
# ext.flutter.imageCache.clear
# ext.flutter.imageCache.size
# ext.flutter.platformOverride
# ext.myapp.clearAuthCache
# ext.myapp.dumpRouterStack

# Get image cache stats
fdb ext call ext.flutter.imageCache.size

# Switch platform overlay to iOS
fdb ext call ext.flutter.platformOverride --arg value=iOS

# Invoke an app-specific extension that collects leak reports (see fdb #46)
fdb ext call ext.flutter.collectLeaks

Memory & heap (pure VM service — no fdb_helper needed)

Command	Description
fdb mem [--json]	Per-isolate heap totals (usage, external, capacity)
fdb mem profile --output <file> [--isolate <id>] [--all-isolates]	Capture a full allocation profile to a JSON file
fdb mem diff <before.json> <after.json> [--sort count|bytes] [--top N] [--all] [--json]	Show classes that grew between two profiles
fdb gc [--json]	Force a full garbage collection across all isolates

Three-tier heap workflow:

1. fdb mem — inspect live per-isolate heap state (usage, external, capacity) to get a quick health check.
2. fdb mem profile --output before.json — capture a full allocation-profile snapshot as a baseline before exercising the feature under test.
3. fdb mem profile --output after.json followed by fdb mem diff before.json after.json — compare the two snapshots to see exactly which classes grew in instance count or byte size.

Utility

Command	Description
fdb skill	Print the AI agent skill file (SKILL.md)
fdb --version	Print the fdb version

Global options

Option	Description
fdb --session-dir <path> <command>	Use a specific .fdb/ session directory instead of auto-resolving

fdb automatically locates the active .fdb/ session by walking up from the current directory, so you can run any command from a subdirectory without changing to the project root. Pass --session-dir to override this and point at a specific session directory.

Widget Interaction (tap, input, scroll)

Requires fdb_helper in your app:

# pubspec.yaml
dev_dependencies:
  fdb_helper: ^1.5.1

// main.dart
import 'package:fdb_helper/fdb_helper.dart';
import 'package:flutter/foundation.dart';

void main() {
  if (!kReleaseMode) {
    FdbBinding.ensureInitialized();
  }
  runApp(MyApp());
}

Troubleshooting

fdb: command not found - Add ~/.pub-cache/bin to your PATH.

Launch hangs - Check the device ID (fdb devices) and the project path.

Screenshot fails - check the tool for your platform is on PATH: adb (Android), xcrun (iOS simulator), screencapture (macOS), xdotool + import (Linux X11). Physical iOS, Windows, and Linux Wayland use fdb_helper — add it to your app and call FdbBinding.ensureInitialized().

Empty widget tree - App may still be starting. Retry, or use fdb describe instead.

RUNNING=false right after launch - The process crashed. When the log contains a recognisable failure, fdb launch prints LAUNCH_ERROR=<CATEGORY>, LAUNCH_ERROR_CAUSE=<description>, and HINT: <remediation> to stderr so you can act on it directly without reading the raw log. If the category is UNKNOWN, inspect the flutter run output above for the first error near the end. See also fdb logs --last 50.

RUNNING=false when running from a subdirectory - fdb walks up the directory tree to find the nearest .fdb/ session automatically. If it still shows RUNNING=false, the app may not be running or the session has a stale PID. Use fdb --session-dir <project>/.fdb status to point directly at the session directory.

Widget interaction fails - fdb_helper missing from pubspec.yaml, or FdbBinding.ensureInitialized() not called.

Agent setup fails mid-flow - Run fdb doctor to check app process, VM service reachability, fdb_helper, platform tools, and stored device state before continuing.

Contributing

See AGENTS.md for coding conventions and the testing skill for running the test suite.

License

MIT