LogViewer

Windows desktop viewer for NLog, log4net, and log4j logs. It receives Chainsaw / NLogViewer XML over UDP or TCP, imports text files and archives, and keeps a large in-memory buffer usable while you filter, search, and jump around.

The interface is in Russian and English. Current release line: 1.2.8.

Download

Requires Windows and .NET Framework 4.8. Windows 10 version 1903 and later, and Windows 11, already include that runtime. The build published on SourceForge.

Features

Live receivers

• UDP and TCP listeners for Chainsaw / NLogViewer / log4j XML. Several ports at once; each receiver has its own color.
• TCP accepts multiple clients on one port (NLog NLogViewer, address="tcp://host:port"). An event split across TCP segments is reassembled before it is parsed.
• Start and stop receivers without closing the app. Ignored IP addresses are dropped on arrival.
• Per-logger Don't receive skips events before they enter the buffer. Optional split of the logger tree by receiver port.

Import

• .txt and .log by a layout template, including NLog layouts. Drag-and-drop, command line, and Open with.
• .zip and .rar, including nested folders. Logs are extracted next to the archive, parsed, then the extract folder is removed.
• Tail of a large file: the whole file, the last N megabytes, or the last N hours relative to the last record.
• Optional live follow: new lines appended to an imported file show up in the list.

Find and narrow

• Logger tree with show, hide, and don't-receive. Minimum level and a time interval.
• Search as plain text or regex, with match case, whole word, and an optional level. Matches run across message, logger, address, thread, executable, throwable, and MDC properties, and are highlighted in the message column.
• Separate results window (Ctrl+Shift+F). Double-click a hit to select that row in the main list.
• Named filter presets: minimum level, search, and selected loggers, applied in one step. Stored in filter_presets.xml next to settings.
• Jump to a timestamp, the next warning, or the next error.

Work with the list

• Bookmarks with a comment, a jump list, and Ctrl+B.
• Copy the selected rows (Ctrl+C).
• Export (Ctrl+S) writes the currently visible, filtered rows to a text file.
• Session (Ctrl+Shift+S / Ctrl+O) saves a file you choose (.lvs or gzip .lvs.gz): the log buffer, bookmarks with comments, hidden loggers, and Don't Receive. The file is never written to Documents on its own.
• Logger statistics: counts, share, levels, last write time, and a jump into the message.
• Repeats window: identical messages grouped by level, logger, and normalized text (GUIDs, dates, and long numbers folded away). Count, first and last time, jump to either end. The main list stays expanded.
• Timeline under the list: message density in the background, Warn / Error / Fatal stacked on the same buckets. A click jumps to the first message in that interval.
• Highlight rules: a persistent row color by level, logger, or message text (substring or regex), with adjustable opacity. Rule order is priority. Rules color rows only; they do not filter the list and they ignore the current search.

Appearance

• Themes and a custom font color.
• Font family and size for the list and the details pane.
• Show or hide the source and thread columns. Date format, tray icon, single instance, and a cap on the in-memory buffer.
• Follow keeps the list scrolled to the newest row. Turn it off to stay put while new logs arrive.

Send logs

Add a receiver in Settings → Receivers (a new receiver defaults to port 7071), then start it.

NLog, UDP:

<target name="viewer" xsi:type="NLogViewer" address="udp://127.0.0.1:7071" />

NLog, TCP:

<target name="viewer" xsi:type="NLogViewer" address="tcp://127.0.0.1:7071" />

log4net:

<appender name="UdpAppender" type="log4net.Appender.UdpAppender">
  <remoteAddress value="127.0.0.1" />
  <remotePort value="7071" />
  <layout type="log4net.Layout.XmlLayoutSchemaLog4j">
    <locationInfo value="true" />
  </layout>
</appender>

The same XML event format is what Chainsaw and log4j socket appenders emit.

Keyboard shortcuts

Shortcut	Action
Ctrl+F	Search and filter the main list
Ctrl+Shift+F	Search results in another window
Shift+F / Shift+D	Next / previous match
Shift+R	Clear the search
Ctrl+R	Clear all logs
Ctrl+S	Export the visible rows to a text file
Ctrl+Shift+S	Save a session
Ctrl+O	Open a session
Ctrl+W / Ctrl+E	Next warning / next error
Ctrl+T	Go to a timestamp
Ctrl+Shift+T	Set the time interval
Ctrl+B	Toggle a bookmark on the selected rows
Ctrl+C	Copy the selected rows

Where files live

File	Location
settings.xml	%Documents%\LogViewer\, or next to the executable if that copy exists and Documents does not
filter_presets.xml	Same folder as settings
template_import_settings.xml	Same folder as settings
Session (.lvs, .lvs.gz)	Whatever path you pick in Save / Open

Screenshots

Search in the main list:

Log entry and logger dialogs:

Settings — general, receivers, ignored addresses:

Build

Open src/LogViewer.sln in Visual Studio 2022 with the .NET desktop development workload, restore NuGet packages, and build. The app targets .NET Framework 4.8.

src/LogViewer.sln
src/LogViewer.csproj            WPF UI, settings, commands
src/LogViewer.Core/             parsers, filter, receivers, session (no UI)
src/LogViewer.Core.Tests/       NUnit
src/LogViewer.App.Tests/        view-model tests

Domain logic belongs in LogViewer.Core. The WPF project stays on UI, settings, and commands.

dotnet test src/LogViewer.Core.Tests/LogViewer.Core.Tests.csproj
dotnet test src/LogViewer.App.Tests/LogViewer.App.Tests.csproj

Tests cover parsers, filtering, receivers, and view-model behavior. They do not cover XAML, ClickOnce, or a live UDP socket.

License

GNU GPL-3.0. You can use, modify, and share this program under that license; derivative work stays under GPL-3.0.

Issues and pull requests are welcome on GitHub.