Taillight (Real-Time Log Viewer)

taillight (you may alias as tl) is a fast, terminal-based log viewer written in Rust. It tail-indexes growing logs in real-time, performing lazy offsets parsing (JSON or plaintext), and renders them in top-bar tabs and tmux-like split layouts.

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Key Features

1. Lazy Tail Indexing: Background indexing of log file offsets keeps memory usage low and scrolling instantaneous, even on gigabyte-sized files.
2. Tmux-like Split Layouts: Split your viewport vertical, horizontal, or in a 2x2 grid to watch different filters simultaneously.
3. Structured Log Parsing: Automatically detects and parses JSON formatted logs (level, message, time) and standard plaintext log severities ([INFO], [ERROR], etc.).
4. Real-time Filters: Add (f), delete (x/c), or rename (r) filters on-the-fly. Filters filter background offsets in concurrent tasks, avoiding UI freeze.
5. Interactive Highlight: Highlight text patterns using regex (s) and jump between matching lines (n/N).
6. Flexible Config Loading & Export: Load settings automatically from local directory or user home config files, with interactive exports (e).

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Installation & Building

Make sure you have Rust and Cargo installed, then run:

cargo build --release

The compiled binary will be generated at ./target/release/taillight.

Tip

You can create a shell alias tl to invoke taillight easily:

alias tl="./target/release/taillight"

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Basic Usage

1. View a Log File

taillight path/to/app.log

2. Stream Stdin (Piped mode)

tail -f app.log | taillight

3. Load with Custom Layout

Override the default layout using the -l or --layout option (single, vertical, horizontal, grid / split2x2):

taillight app.log -l grid

4. Load with Specific Config Path

By default, taillight looks for taillight_config.json in the current working directory, then in home folders. You can pass a specific path using -c / --config:

taillight app.log -c custom_rules.json

5. Hide Timestamps on Startup

You can launch taillight with the --no-timestamps flag to hide parsed timestamps:

taillight app.log --no-timestamps

6. Control Ctrl-C Behavior (Piped Mode)

By default, pressing Ctrl-C kills both the writing process in the pipeline and exits taillight. You can change this using --ctrl-c-behavior to only kill the writer process, allowing you to browse the captured logs in TUI:

# Keep taillight open after Ctrl-C stops the stream
some_generator | taillight --ctrl-c-behavior kill-writer

7. Enable Word Wrapping

You can start taillight with word wrapping enabled using -w or --word-wrap option:

taillight app.log -w

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5. Case-Insensitivity Tips

• Log Levels (Trace, Debug, Info, Warn, Error, Fatal): taillight's built-in log level classifier is completely case-insensitive by default. Values like [info], [Info], or [INFO] (as well as JSON level values like "warning", "Warn", etc.) are detected and filtered identically.
• Regex Filters & Highlights (/ and s keys): Custom regular expression filters on tabs or highlight queries are case-sensitive by default. To perform case-insensitive keyword filtering or highlighting, prepend your regex with the (?i) modifier (e.g. (?i)stripe will match stripe, Stripe, or STRIPE).

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Interactive Hotkeys

When in Normal Mode:

Key	Action
q	Quit the application cleanly
? / H	Show the quick help bar
/	Edit active filter's regex pattern
s	Set/edit regex highlight query for the active pane
n / N	Jump forward/backward to the next highlight match
f	Create a custom filter (prompts for Name and Regex filter)
t	Toggle time display (show/hide timestamps) on the fly
C	Toggle Ctrl-C behavior (Kill All & Exit / Kill Writer Only) on the fly
w	Toggle word wrapping (show wrapped lines) on the fly
r	Rename the current filter
x / c	Delete the current filter (except system default filters)
e	Export current view config (prompts for destination filename)
v	Cycle layout modes (Single, SplitVertical, SplitHorizontal, Split2x2)
Tab	Switch focus forward to the next pane
Shift + Tab	Switch focus backward to the previous pane
h / l or ← / →	Cycle active filter index in the current pane
j / k or ↓ / ↑	Scroll logs down/up by 1 line
Ctrl + d / Ctrl + u	Scroll logs down/up by half-screen
g / G	Jump to the very beginning / end of logs
0 to 9	Jump directly to filter index 0-9 in the active pane
Esc	Clear active prompts or return to Normal Mode

For more details on setting up custom layouts and filter rules, see config.md.