How do I format a Java stack trace?

Paste your Java stack trace into Debugly's input area. The tool automatically detects Java exceptions, formats them into a readable tree, highlights the root cause exception, and identifies your application's frames versus library frames. You can also filter by package namespace.

What causes "Traceback (most recent call last)" in Python?

"Traceback (most recent call last)" is Python's standard header for exception reports. It appears whenever an unhandled exception occurs. The frames are listed oldest-first (least recent at top), with the actual error type and message on the final line.

How do I read a stack trace?

Start from the bottom of a stack trace to find the root cause exception. Then read upward through the frames to trace the call chain that led to the error. In Java, look for lines starting with 'at' that reference your own code (not library code). In Python, the error is on the last line after the traceback frames.

What is a free online stack trace formatter?

Debugly (debugly.pages.dev) is a free, browser-based stack trace formatter that supports Java, Kotlin, Scala, and Python. It parses raw error logs, formats them into readable trees, identifies root causes, and runs entirely client-side so no data is sent to a server.

How do I parse an error log?

Copy your error log text and paste it into Debugly's input panel. The tool automatically detects the language (Java or Python), extracts the stack trace, and formats it with root cause analysis. You can filter frames by package namespace to focus on your application code.

Does Debugly send my stack trace to a server?

No. Debugly processes all stack traces entirely in your browser using client-side JavaScript. No trace data is ever transmitted to a server. Shareable URLs use client-side compression and encode the trace data in the URL fragment.

Stack Trace Formatter - Stop squinting at logs

stack-trace.txt

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about

Free Online Stack Trace Formatter & Parser

Debugly is a free, client-side stack trace formatter and parser for Java, Kotlin, Scala, and Python. All processing happens in your browser — no data is sent to a server.

How it works

Paste your stack trace into the input area
Auto-detect language or manually select JAVA/PY
Optionally filter by package namespace
Review formatted output and root cause analysis

What is a stack trace?

A stack trace is a report of the active stack frames at a specific point during program execution, typically shown when an error or exception occurs. It shows the sequence of method calls that led to the error.

Java stack traces

Java stack traces begin with an exception class and message, followed by "at" lines listing class, method, file, and line number. Debugly formats these into a readable tree and highlights the root cause exception.

Python tracebacks

"Traceback (most recent call last)" is Python's standard error header. Frames are listed oldest-first, with the error type and message on the last line. Debugly parses and reformats these for easy reading.

Supported languages

Java
Kotlin
Scala
Python

Privacy

All processing is client-side in your browser. No stack trace data is ever sent to a server. You can share traces with colleagues using compressed URLs generated locally.

FAQ

What does "Traceback (most recent call last)" mean?: It is Python's standard prefix for an exception report. The most recent (innermost) call appears last, just above the error line.
How do I filter out library frames?: Type your package namespace (e.g. "com.mycompany") into the namespace field in the top-right of the output panel to show only your code's frames.
Can I share a stack trace with a colleague?: Yes. After pasting a trace, the URL updates automatically with a compressed version of your trace. Copy and share the URL.
Is my data safe?: Yes. Debugly runs entirely in your browser. No data leaves your machine.

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