Skip to content
SPECIFICTION
Get listed

FLEX

engineering.flipboard.com

Free plan iOS
Visit engineering.flipboard.com
Spec score 8.5 #4 of 27 in Debuggers

What it is

FLEX is a free, open-source debugging and exploration library for iOS applications. It runs inside the app and places a toolbar in a window above it, allowing developers to inspect and change application state without an LLDB or Xcode connection or a remote debugging server. The tool can inspect view hierarchies, find live heap objects, show and modify properties and ivars, and call methods. Its network history covers NSURLConnection and NSURLSession requests with timing, headers, and responses. Developers can browse app bundles and sandboxes, inspect SQLite and Realm databases, and view or edit NSUserDefaults values, including strings, numbers, arrays, and dictionaries. FLEX works in the iOS Simulator and on physical devices, supports Objective-C and Swift, and requires an iOS 9-or-later target. Installation options include CocoaPods, Carthage, Buck, manual Xcode integration, and Swift Package Manager.

Spec sheet

Purpose
FLEX is an in-app debugging and exploration tool for iOS development.Read 8 Oct 2026 · engineering.flipboard.com
Intended users
The maker describes FLEX as a tool for iOS development and debugging.Read 7 Oct 2026 · github.com
Founded
2014Read 28 Sep 2026 · engineering.flipboard.com
App settings
It can view and dynamically modify NSUserDefaults values.Read 7 Oct 2026 · github.com
Contributions
The project welcomes pull requests and directs contributors to its contributing guide.Read 8 Oct 2026 · engineering.flipboard.com
Device use
The maker says FLEX works in the simulator and on physical devices.Read 7 Oct 2026 · engineering.flipboard.com
File and database browsers
It can browse the app’s sandbox files and SQLite or Realm databases.Read 8 Oct 2026 · github.com
File and database browsing
FLEX can browse the app bundle or sandbox, and explore SQLite and Realm databases.Read 7 Oct 2026 · github.com
Heap exploration
FLEX can scan live allocated memory for objects and let developers inspect them.Read 8 Oct 2026 · github.com
How it works
It presents a toolbar in a window above the running app, where developers can view and modify application state.Read 7 Oct 2026 · github.com
In-app toolbar
It displays a toolbar in a window above the app, where developers can view and modify application state.Read 8 Oct 2026 · github.com
Installation
The project documents installation through CocoaPods, Carthage, Buck, manual Xcode integration, and Swift Package Manager.Read 8 Oct 2026 · github.com
License and contributions
Flipboard announced FLEX as open source and welcomed pull requests.Read 7 Oct 2026 · engineering.flipboard.com
Minimum target
FLEX requires an app that targets iOS 9 or higher.Read 8 Oct 2026 · github.com
Network debugging
Its network history can show requests made using NSURLConnection or NSURLSession, including timing, headers, and responses.Read 7 Oct 2026 · github.com
Network history
Network debugging can show request timing, headers, and full responses for requests made using NSURLConnection or NSURLSession.Read 8 Oct 2026 · github.com
NSUserDefaults
Developers can view and dynamically modify NSUserDefaults values; supported editable values include strings, numbers, arrays, and dictionaries.Read 8 Oct 2026 · github.com
Object inspection
It can find live objects on the heap, show their properties and ivars, modify them, and call methods.Read 7 Oct 2026 · github.com
Operation
FLEX runs inside the app and works in both the simulator and on physical devices without an LLDB/Xcode connection or remote debugging server.Read 8 Oct 2026 · engineering.flipboard.com
Platform limit
FLEX does not support tvOS out of the box.Read 7 Oct 2026 · github.com
Release-build caution
The project advises excluding FLEX from Release builds because exposing the tool to app users is not recommended and may cause App Store rejection.Read 8 Oct 2026 · github.com
Runtime requirement
FLEX runs inside the app and does not require LLDB, Xcode, or a remote debugging server connection while in use.Read 7 Oct 2026 · engineering.flipboard.com
tvOS support
FLEX does not support tvOS out of the box; the project points users to third-party forks for ports.Read 8 Oct 2026 · github.com
View inspection
Developers can inspect and modify views in the hierarchy and examine object properties and instance variables.Read 8 Oct 2026 · github.com

Plans and prices

FLEX Free Open-source iOS debugging library · iOS 9 or higher Read 8 Oct 2026 · github.com

Every FLEX plan and price →

Strong points and limits

Strong points

  • Free open-source iOS library
  • Runs without remote debugging
  • Inspects views and heap objects
  • Browses SQLite and Realm databases
  • Works on physical iOS devices

Limits

  • Requires an iOS 9-or-later target
  • No tvOS support out of the box
  • Release builds should exclude FLEX
  • No free trial listed

Who it suits

FLEX is aimed at iOS developers debugging applications written in Objective-C or Swift. It suits teams needing in-app inspection on simulators or physical devices.

Verdict

FLEX puts extensive inspection controls inside an iOS app, covering interface state, objects, requests, files, databases, and preferences. Its in-app design avoids LLDB, Xcode, and remote-server connections, but requires care around Release builds and does not provide built-in tvOS support.

Where Specifiction places it

Alternatives to FLEXAll alternatives →