Log Viewer Ultra

A custom editor for .log files that renders ANSI escape sequences as real colour, highlights lines with filter rules you define, and stays responsive on multi-gigabyte files. Parsing, ANSI rendering, filtering and search run in a Rust core compiled to WebAssembly; large files are indexed on a background worker thread and only the visible window is rendered.

Features

• Opens .log files automatically. The custom editor claims the filename patterns *.log and *.log.* at default priority, so plain logs and rotated ones (app.log.1, service.log.2026-08-16) open in the viewer rather than the text editor. Open in Text Editor — a button in the toolbar and in the editor title bar — switches back at any time, and Log Viewer Ultra: Open in Log Viewer goes the other way.

• ANSI rendering. SGR sequences become styled HTML: the 8 standard and 8 bright foreground/background colours, 256-colour (38;5;n / 48;5;n), 24-bit truecolor (38;2;r;g;b), and bold, dim, italic, underline, inverse and strikethrough. The 16 named colours map to VS Code's --vscode-terminal-ansi* variables, so they follow your theme rather than being hard-coded. Style state carries across line boundaries the way a terminal handles it. Everything that is not SGR is quietly stripped — cursor moves and screen clears (ESC [ 2K, ESC [ H, ESC [ ?25l), OSC sequences including hyperlinks and window titles, DCS/SOS/PM/APC, charset designators, and bare carriage returns. CRLF is normalised to LF. Turn rendering off with the ANSI toolbar button to see the raw text with the escapes still stripped.

• Filter rules colour whole lines. A rule is a substring or a JavaScript regular expression, case-insensitive by default, with a CSS colour used as the line's background. Each line is tagged with the first rule that matches it. Out of the box — when you have configured neither logViewer.filterSets nor logViewer.filters — a built-in Log Levels set is used:

  Rule	Pattern	Case	Colour
  Error	\b(ERROR\|FATAL\|CRITICAL\|SEVERE)\b	sensitive	#5a1f1f
  Warn	\bWARN(ING)?\b	sensitive	#5a4a1f
  Info	\bINFO\b	sensitive	#1f4a5a
  Debug	\bDEBUG\b	sensitive	#3a3a3a
  Trace	\bTRACE\b	sensitive	#2f1f5a

  So a log like this gets three coloured lines and one plain one:

  2026-08-16 09:12:44.108 INFO  [main] c.e.Bootstrap - starting, pid=4181
  2026-08-16 09:12:44.902 DEBUG [pool-1] c.e.db.Pool - opened 8 connections
  2026-08-16 09:12:45.331 WARN  [pool-1] c.e.db.Pool - slow acquire: 412ms
  2026-08-16 09:12:45.334 ERROR [http-7] c.e.api.Handler - upstream timeout
      at com.example.api.Handler.dispatch(Handler.java:118)
  

  Note that the highlight is per line and comes only from the rules — nothing else in the line is parsed. Timestamps, thread names, logger names, stack frames, JSON payloads, URLs and IP addresses are not recognised or coloured on their own; if you want them marked, write a rule for them.

• Filter sets. Rules are grouped into named sets you can switch on and off from the Sets dropdown — one set for a login flow, one for audio, one for whatever you are chasing today. Individual rules also appear as chips on the toolbar; click a chip to mute that rule without touching the set. Toggles made this way last for the editor session; the persisted defaults live in logViewer.filterSets.

• A filter editor. Log Viewer Ultra: Edit Filter Sets (also reachable from the Sets dropdown) opens a modal for creating sets and rules, with name, pattern, regex and case-sensitivity fields, a 16-swatch colour palette plus a colour picker for adding your own, and regex validation on save. Saving writes to workspace settings when a workspace is open, otherwise to user settings; custom palette colours go to logViewer.colorPalette. If no log viewer is open, the command opens the settings UI instead.

• Two filter modes. In Highlight mode every line is shown and matching lines get their rule's background. In Only matching mode the view collapses to just the lines that match an enabled rule. The Highlight / Only matching toolbar button switches between them.

• Search. The search box does substring or regex matching, with independent .* (regex) and Aa (case-sensitive) toggles, a match count, and <mark> highlighting of the matched substrings that survives the ANSI markup around them. Search composes with the filter mode: in Only matching mode you see the intersection of the search hits and the enabled rules. Escape clears the box.

• Virtualised rendering. Only the lines on screen (plus a small overscan) are in the DOM, so scrolling a large log stays smooth. Optional word wrap, an optional left gutter with the original file line number, and a font size independent of the editor's are all toggleable from the toolbar or by command. The A+ / A− / A0 buttons and the font-size commands step within 8–36 px.

• Large files stream. Above logViewer.streamingThresholdBytes (4 MB by default) the extension switches pipelines: a worker thread scans the file and records a byte offset every 1024 lines, and the viewer asks the host for 200-line windows as you scroll, reading and rendering just those bytes. The first and last megabyte are pre-rendered at open, so the first page and the End ⏭ button work before indexing has finished. A banner reports indexing progress; filter and search passes run incrementally over the whole file and stream their hits in as they are found (capped at 1,000,000 hits, after which the banner says so). Ctrl+End / Cmd+End jumps to the end of the file and Ctrl+Home / Cmd+Home to the start.

• Change detection. While a streamed file is open, the extension watches it and shows a File changed on disk (+12.4 KB) banner with a Reload button when its size or mtime moves. This is a prompt, not a live tail — the view does not follow the file until you reload.

• The line index can be cached. By default it is kept in memory only and rebuilt on the next open, which is fast because it is tiny (about 8 bytes per 1024 lines). logViewer.indexLocation can instead persist it to the extension's global storage, next to the log file, or to a directory you choose, so reopening a huge log skips the scan entirely. Log Viewer Ultra: Clear Index Cache empties the global-storage and custom directories; index files written next to logs are left alone.

Settings

The view settings (renderAnsi, wordWrap, lineNumbers, fontSize, filterMode) are the starting state for each editor. The matching toolbar buttons and commands change the open view only; edit the setting to change the default.

Commands

All commands are under the Log Viewer Ultra category.

• Open in Log Viewer Ultra (logViewer.openInLogViewer) — reopen the active text editor's document in the viewer.
• Open in Text Editor (logViewer.openInTextEditor) — reopen the active document in the default text editor. Also a button in the editor title bar.
• Toggle ANSI Color Rendering (logViewer.toggleAnsi)
• Toggle Word Wrap (logViewer.toggleWrap)
• Toggle Line Numbers (logViewer.toggleLineNumbers)
• Toggle Filter Mode (Highlight / Only Matching) (logViewer.toggleFilterMode)
• Focus Search Box (logViewer.focusSearch)
• Increase Font Size (logViewer.fontSizeIncrease)
• Decrease Font Size (logViewer.fontSizeDecrease)
• Reset Font Size (logViewer.fontSizeReset)
• Edit Filter Sets (logViewer.editFilterSets) — open the filter set editor, or the settings UI if no log viewer is active.
• Clear Index Cache (logViewer.clearIndexCache) — delete persisted index files from the global storage and custom index directories.

Keyboard shortcuts

These are active while a Log Viewer Ultra editor has focus.