LLDB Command Reference Complete command reference for LLDB in Xcode. Organized by task so you can find the exact command you need. For debugging workflows and decision trees, see /skill axiom-lldb . Part 1: Variable Inspection v / frame variable Reads memory directly. No compilation. Most reliable for Swift values. (lldb) v # All variables in current frame (lldb) v self # Self in current context (lldb) v self.propertyName # Specific property (lldb) v localVariable # Local variable (lldb) v self.array[0] # Collection element (lldb) v self._showDetails # SwiftUI @State backing store (underscore prefix) Flags: Flag Effect -d run Run dynamic type resolution (slower but more accurate) -T Show types -R Show raw (unformatted) output -D N Limit depth of nested types to N levels -P N Limit pointer depth to N levels -F Flat output (no hierarchy) Limitations: Cannot evaluate expressions, computed properties, or function calls. Use p for those. p / expression (with format) Compiles and executes an expression. Shows formatted result. (lldb) p self.computedProperty (lldb) p items.count (lldb) p someFunction() (lldb) p String(describing: someValue) (lldb) p (1...10).map { $0 * 2 } Result stored in numbered variables: (lldb) p someValue $R0 = 42 (lldb) p $R0 + 10 $R1 = 52 po / expression --object-description Calls debugDescription (or description ) on the result. (lldb) po myObject (lldb) po error (lldb) po notification.userInfo (lldb) po NSHomeDirectory() When po adds value: Classes with CustomDebugStringConvertible , NSError , NSNotification , collections of objects. When po fails: Swift structs without CustomDebugStringConvertible , protocol-typed values (use v instead — it performs iterative dynamic type resolution that po doesn't). expression (full form) Full expression evaluation with all options. (lldb) expression self.view.backgroundColor = UIColor.red (lldb) expression self.debugFlag = true (lldb) expression myArray.append("test") (lldb) expression CATransaction.flush() # Force UI update (lldb) expression Self._printChanges() # SwiftUI debug Flags: Flag Effect -l objc Evaluate as Objective-C -l swift Evaluate as Swift (default) -O Object description (same as po ) -i false Stop on breakpoints hit during evaluation (default: ignore) -- Separator between flags and expression ObjC expressions for Swift debugging: (lldb) expr -l objc -- (void)[[[UIApplication sharedApplication] keyWindow] recursiveDescription] (lldb) expr -l objc -- (void)[CATransaction flush] (lldb) expr -l objc -- (int)[[UIApplication sharedApplication] _isForeground] register read Low-level register inspection: (lldb) register read (lldb) register read x0 x1 # Specific registers (ARM64) (lldb) register read --all # All register sets Part 2: Breakpoints Setting Breakpoints (lldb) breakpoint set -f File.swift -l 42 # File + line (lldb) b File.swift:42 # Short form (lldb) breakpoint set -n methodName # By function name (lldb) breakpoint set -n "MyClass.myMethod" # Qualified name (lldb) breakpoint set -S layoutSubviews # ObjC selector (lldb) breakpoint set -r "viewDid.*" # Regex on name (lldb) breakpoint set -a 0x100abc123 # Memory address Conditional Breakpoints (lldb) breakpoint set -f File.swift -l 42 -c "value == nil" (lldb) breakpoint set -f File.swift -l 42 -c "index > 100" (lldb) breakpoint set -f File.swift -l 42 -c 'name == "test"' Ignore Count (lldb) breakpoint set -f File.swift -l 42 -i 50 # Skip first 50 hits One-Shot Breakpoints (lldb) breakpoint set -f File.swift -l 42 -o # Delete after first hit Breakpoint Commands (Logpoints) Add commands that execute when breakpoint hits: (lldb) breakpoint command add 1

v self.state p self.items.count continue DONE Or in one line: (lldb) breakpoint command add 1 -o "v self.state" Exception Breakpoints (lldb) breakpoint set -E swift # All Swift errors (lldb) breakpoint set -E objc # All ObjC exceptions

Filtering by exception name requires Xcode's GUI (Edit Breakpoint → Exception field)

Symbolic Breakpoints (lldb) breakpoint set -n UIViewAlertForUnsatisfiableConstraints # Auto Layout (lldb) breakpoint set -n "-[UIApplication _run]" # App launch (lldb) breakpoint set -n swift_willThrow # Swift throw Managing Breakpoints (lldb) breakpoint list # List all (lldb) breakpoint list -b # Brief format (lldb) breakpoint enable 3 # Enable breakpoint 3 (lldb) breakpoint disable 3 # Disable breakpoint 3 (lldb) breakpoint delete 3 # Delete breakpoint 3 (lldb) breakpoint delete # Delete ALL (asks confirmation) (lldb) breakpoint modify 3 -c "x > 10" # Add condition to existing Watchpoints Break when a variable's memory changes: (lldb) watchpoint set variable self.count # Watch for write (lldb) watchpoint set variable -w read_write myGlobal # Watch for read or write (lldb) watchpoint set expression -- &myVariable # Watch memory address (lldb) watchpoint list # List all (lldb) watchpoint delete 1 # Delete watchpoint 1 (lldb) watchpoint modify 1 -c "self.count > 10" # Add condition Note: Hardware watchpoints are limited (~4 per process). Use sparingly. Part 3: Thread & Backtrace Backtraces (lldb) bt # Current thread backtrace (lldb) bt 10 # Limit to 10 frames (lldb) bt all # All threads (lldb) thread backtrace all # Same as bt all Thread Navigation (lldb) thread list # List all threads with state (lldb) thread info # Current thread details + stop reason (lldb) thread select 3 # Switch to thread 3 Frame Navigation (lldb) frame info # Current frame details (lldb) frame select 5 # Jump to frame 5 (lldb) up # Go up one frame (toward caller) (lldb) down # Shortcut: go down one frame Thread Return (Skip Code) Force an early return from the current function: (lldb) thread return # Return void (lldb) thread return 42 # Return specific value Use with caution — skips cleanup code, can leave state inconsistent. Part 4: Expression Evaluation Swift Expressions (lldb) expr let x = 42; print(x) (lldb) expr self.view.backgroundColor = UIColor.red (lldb) expr UIApplication.shared.windows.first?.rootViewController (lldb) expr UserDefaults.standard.set(true, forKey: "debug") Objective-C Expressions Switch to ObjC when Swift expression parser fails: (lldb) expr -l objc -- (void)[CATransaction flush] (lldb) expr -l objc -- (id)[[UIApplication sharedApplication] keyWindow] (lldb) expr -l objc -- (void)[[NSNotificationCenter defaultCenter] postNotificationName:@"test" object:nil] UI Debugging Expressions (lldb) expr -l objc -- (void)[[[UIApplication sharedApplication] keyWindow] recursiveDescription] (lldb) po UIApplication.shared.windows.first?.rootViewController?.view.recursiveDescription() SwiftUI Debugging (lldb) expr Self._printChanges() # Print what triggered body re-eval (inside view body only) Runtime Type Information (lldb) expr type(of: someValue) (lldb) expr String(describing: type(of: someValue)) Part 5: Process Control Execution Control (lldb) continue # Resume execution (c) (lldb) c # Short form (lldb) process interrupt # Pause running process (lldb) thread step-over # Step over (n / next) (lldb) n # Short form (lldb) thread step-in # Step into (s / step) (lldb) s # Short form (lldb) thread step-out # Step out (finish) (lldb) finish # Short form (lldb) thread step-inst # Step one instruction (assembly-level) (lldb) ni # Step over one instruction Process Management (lldb) process launch # Launch/restart (lldb) process attach --pid 1234 # Attach to running process (lldb) process attach --name MyApp # Attach by name (lldb) process detach # Detach without killing (lldb) kill # Kill debugged process Part 6: Memory & Image Memory Reading (lldb) memory read 0x100abc123 # Read memory at address (lldb) memory read -c 64 0x100abc123 # Read 64 bytes (lldb) memory read -f x 0x100abc123 # Format as hex (lldb) memory read -f s 0x100abc123 # Format as string Memory Search (lldb) memory find -s "searchString" -- 0x100000000 0x200000000 Image/Module Inspection (lldb) image lookup -a 0x100abc123 # Lookup symbol at address (lldb) image lookup -n myFunction # Find function by name (lldb) image lookup -rn "MyClass.*" # Regex search (lldb) image list # List all loaded images/frameworks (lldb) image list -b # Brief format Common use: Finding which framework a crash address belongs to: (lldb) image lookup -a 0x1a2b3c4d5 Part 7: .lldbinit & Customization File Location LLDB reads ~/.lldbinit at startup. Per-project init files are also supported when configured in Xcode's scheme settings. Useful Aliases Add to ~/.lldbinit :

Quick reload — flush UI changes made via expression

command alias flush expr -l objc -- (void)[CATransaction flush]

Print view hierarchy

command alias views expr -l objc -- (void)[[[UIApplication sharedApplication] keyWindow] recursiveDescription]

Print auto layout constraints

command alias constraints po [[UIWindow keyWindow] _autolayoutTrace] Custom Type Summaries

Show CLLocationCoordinate2D as "lat, lon"

type summary add CLLocationCoordinate2D --summary-string "${var.latitude}, ${var.longitude}"

Settings

(lldb) settings show target.language # Current language

(lldb) settings set target.language swift # Force Swift mode

(lldb) settings set target.max-children-count 100 # Show more collection items

Per-Project .lldbinit

In Xcode: Edit Scheme → Run → Options → "LLDB Init File" field.

Put project-specific aliases and breakpoints in a

.lldbinit

file in your project root.

Part 8: Troubleshooting LLDB Itself

"expression failed to parse"

Cause:

Swift expression parser can't resolve types from the current module.

Fixes:

Use

v

instead (no compilation needed)

Simplify the expression

Try

expr -l objc -- ...

for ObjC-bridge types

Clean derived data and rebuild

"variable not available"

Cause:

Compiler optimized the variable out.

Fixes:

Switch to Debug build configuration

Set

-Onone

for the specific file (Build Settings → per-file compiler flags)

Use

register read

to check if the value is in a register

"wrong language mode"

Cause:

LLDB defaults to ObjC in some contexts (especially in frameworks).

Fix:

(lldb) settings set target.language swift

(lldb) expr -l swift -- mySwiftExpression

"expression caused a crash"

Cause:

The expression you evaluated had a side effect that crashed.

Fix:

Don't evaluate expressions that modify state unless you intend to

Use

v

for read-only inspection

If the crash corrupted state, restart the debug session

LLDB Hangs or Is Slow

Cause:

Usually compiling a complex expression or resolving types in a large project.

Fix:

Use

v

instead of

p

/

po

(no compilation)

Reduce expression complexity

If LLDB hangs during

po

, Ctrl+C to cancel and use

v

instead

Breakpoint Not Hit

Causes and fixes:

Cause

Fix

Wrong file/line (code moved)

Re-set breakpoint on current code

Breakpoint disabled

breakpoint enable N

Code not executed

Verify the code path is reached

Optimized out (Release)

Switch to Debug configuration

In a framework/SPM package

Set symbolic breakpoint by function name

Resources

WWDC

2019-429, 2018-412, 2022-110370, 2015-402

Docs

/xcode/stepping-through-code-and-inspecting-variables-to-isolate-bugs, /xcode/setting-breakpoints-to-pause-your-running-app

Skills

axiom-lldb, axiom-xcode-debugging