> ## Documentation Index
> Fetch the complete documentation index at: https://docs.nativeline.ai/llms.txt
> Use this file to discover all available pages before exploring further.
# Reading App Logs
> Use logs to debug runtime issues and understand app behavior
# Reading App Logs
**Pro plan or higher required**
Build errors show problems at compile time. But what about issues that happen while your app is running? That's where app logs come in.
## What Are App Logs?
Logs are messages your app produces while running. They show:
* What code is executing
* Values of variables
* Errors that occur at runtime
* User actions and their effects
***
## Accessing Logs in Nativeline
Click the **Code Editor** tab in the Nativeline interface.
Find and click the **Logs** tab or section within the Code Editor.
Build and run your app. Logs appear in real-time.
As you interact with your app, logs show what's happening.
***
## Understanding Log Output
### Basic Log Structure
```
2024-01-15 10:30:45.123 MyApp[12345:67890] Save button tapped
2024-01-15 10:30:45.456 MyApp[12345:67890] Saving data: User(name: "John")
2024-01-15 10:30:45.789 MyApp[12345:67890] Save completed successfully
```
Each line shows:
* **Timestamp:** When it happened
* **App name:** Which app
* **Message:** The actual log content
### Log Types
| Type | Meaning |
| ---------------- | ----------------------------------- |
| **Info logs** | Normal operation, status updates |
| **Warning logs** | Something unusual, but not critical |
| **Error logs** | Something went wrong |
| **Debug logs** | Developer debugging info |
***
## Adding Logs to Your App
Ask the AI to add logging:
### For Debugging a Specific Feature
```
Add print statements to the saveData function to show:
- When the function starts
- What data is being saved
- Whether the save succeeded or failed
```
### For Tracking User Actions
```
Add logging for all button taps so I can see what users are doing
```
### For API/Network Issues
```
Add logging to show:
- When API requests start
- What data is being sent
- What response comes back
- Any errors that occur
```
***
## Common Debugging Scenarios
### Debugging "Nothing Happens" Issues
Your button doesn't seem to work? Add logs:
```
Add a print statement at the start of the button's action
to confirm it's being triggered
```
If the log appears: The button works, the issue is in the code after.
If no log appears: The button isn't connected properly.
### Debugging Data Issues
Data not showing up?
```
Add logging to show:
- When data is loaded
- How many items were loaded
- The actual content of the first item
```
Check the logs to see if data exists and what it contains.
### Debugging Navigation Issues
Screen not appearing?
```
Add logging when the navigation to [screen] is triggered
and when [screen] appears
```
Follow the trail to see where it breaks.
### Debugging Crash-Like Behavior
App freezing or behaving strangely?
```
Add extensive logging throughout [feature] to trace exactly
where the problem occurs
```
The last log before the freeze indicates where to look.
***
## Reading Swift Error Messages
When Swift errors appear in logs, they often include useful info:
### Optional Unwrapping Errors
```
Fatal error: Unexpectedly found nil while unwrapping an Optional value
```
**Meaning:** Your code tried to use a nil value that should have had a value.
**Fix:** Ask the AI to add nil checking for the relevant variable.
### Array Index Errors
```
Fatal error: Index out of range
```
**Meaning:** Accessing an array position that doesn't exist.
**Fix:** Check array bounds before accessing, or verify the data exists.
### Type Casting Errors
```
Could not cast value of type 'X' to 'Y'
```
**Meaning:** Tried to convert between incompatible types.
**Fix:** Check the actual type and handle it appropriately.
***
## Effective Logging Strategies
### 1. Log Entry and Exit
```swift theme={null}
print("▶️ saveProfile started")
// ... code ...
print("✅ saveProfile completed")
```
This shows whether functions complete or exit early.
### 2. Log Important Values
```swift theme={null}
print("📊 User data: \(userData)")
print("📊 Items count: \(items.count)")
```
See what your variables actually contain.
### 3. Log Decision Points
```swift theme={null}
if isLoggedIn {
print("🔓 User is logged in, showing profile")
} else {
print("🔒 User not logged in, showing login")
}
```
Understand which code paths execute.
### 4. Use Distinctive Markers
Using emojis or prefixes makes logs easier to scan:
* `▶️` Start of function
* `✅` Success
* `❌` Error
* `⚠️` Warning
* `📊` Data values
* `🔄` State changes
***
## Filtering and Searching Logs
When there's a lot of output:
### Search for Specific Text
Look for your custom log messages or error keywords.
### Filter by Feature
If you're debugging the save feature, search for "save" in logs.
### Filter by Error Level
Look for "error", "failed", "nil", or "crash" to find problems.
***
## When to Use Logs vs Build Errors
| Situation | Check |
| --------------------------------- | ------------------------------- |
| App won't compile | Build errors in chat |
| App compiles but crashes | Runtime logs |
| App runs but feature doesn't work | Runtime logs |
| UI looks wrong | Visual inspection + logs |
| Data doesn't save | Logs showing save operations |
| API not working | Logs showing requests/responses |
***
## Removing Debug Logs
Before publishing your app, clean up debug logs:
```
Remove all the debug print statements we added for troubleshooting.
Keep only important error logging.
```
Or for more control:
```
Replace debug print statements with proper logging that only
shows in debug builds, not in production.
```
***
## Advanced: Console.app
For even more detailed debugging, you can use macOS's Console app:
1. Open **Console.app** (in Applications → Utilities)
2. Select your Simulator in the sidebar
3. Run your app
4. See comprehensive system logs
This shows logs from iOS itself, not just your app.
***
## Troubleshooting
* Make sure your app is running
* Check you're on the Logs tab
* Try adding explicit print statements
* Restart the Simulator
* Add distinctive prefixes to your logs
* Search for specific terms
* Ask the AI to reduce logging: "Only log errors, not normal operations"
The Logs feature requires Pro plan or higher. Check your subscription in Settings.
***
## Next Steps
Complete debugging walkthrough
Full Code Editor documentation