How does level detection work?

Each line is scanned for common level keywords (ERROR, FATAL, WARN/WARNING, INFO, DEBUG) as whole words — it doesn't require a specific structured log format, so it works across most conventional logging styles.

Can I combine a level filter with a text search?

Yes — both filters apply together, so you can narrow down to, for example, only ERROR lines that also contain a specific keyword like a request ID.

Is there a file size limit for uploads?

No hard limit is enforced, but very large log files may take a moment to render fully, since every line is processed in your browser.

Is my log file uploaded to a server?

No — the entire file is read and processed in your browser. Nothing is uploaded anywhere.

Free Online Log File Viewer

Features

Runs entirely in your browser
Privacy-first — your data is never uploaded
Real-time, instant results
100% free, no sign-up required
Works on desktop, tablet, and mobile
No installation needed

Who uses this tool?

Software engineersWeb developersAPI testersDevOps engineersStudents

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About Log File Viewer

Raw log files are dense, uniform walls of text — finding the actual error buried among hundreds of routine INFO lines usually means scrolling and squinting, or writing a quick grep command just to filter down to what matters.

This tool color-codes every log line by its detected level (ERROR and FATAL in red, WARN in amber, INFO in blue, DEBUG muted), shows a count badge for each level found, and lets you click a badge to filter down to just that level, combined with a free-text search box for filtering by keyword.

Level detection works by matching common log level keywords directly in each line's text — it doesn't require a specific log format, so it works reasonably well across server logs, application logs, and most conventional logging output, though logs using non-standard level naming won't be color-coded.

How it works

Paste or upload a log file. Paste log text directly, or upload a .log or .txt file.
Filter by level. Click a level badge (ERROR, WARN, INFO, DEBUG) to filter to just that level.
Search by keyword. Type in the search box to filter lines containing specific text.

Examples

Filtering to errors only

Input

A log with mixed INFO and ERROR lines, click the ERROR badge

Output

Only lines containing "ERROR" are shown, highlighted in red.