loglens

loglens

A terminal UI log viewer with real-time rich formatting. Pipe any command output through loglens and it automatically detects and highlights JSON, Go test results, diffs, Kubernetes resources, tables, timestamps, warnings, and more — with an interactive tree for navigating nested structures.

Features

• JSON detection — inline and multiline JSON is parsed into a navigable tree. Expand/collapse objects and arrays with arrow keys.
• Go test output — === RUN, --- PASS/FAIL/SKIP markers are highlighted with durations and pass/fail color coding.
• Diff highlighting — unified diff hunks get colored add/remove lines and hunk headers.
• Kubernetes resources — kind/name paths (e.g. deployment.apps/my-deploy) and CRD API groups are highlighted.
• Table detection — space-aligned and tab-separated tabular output (e.g. kubectl get) is rendered with aligned separators.
• Timestamps and log levels — ISO 8601 dates, WARN/ERROR/INFO/DEBUG prefixes, and source file references are all styled.
• Follow mode — auto-scrolls to new lines as they arrive, like tail -f.
• Wrap mode — toggle line wrapping for long lines (w key).
• Search — / to enter search mode; n/N to jump between matches.
• Minimap — VS Code-style braille minimap overlay showing your position in the stream (m to toggle).
• Large file support — disk-offloaded chunked store handles streams well beyond available RAM; O(log N) Fenwick-tree-backed scrolling stays fast at 100K+ lines.

Installation

go install github.com/wufe/loglens@latest

Usage

Pipe mode

kubectl logs -f my-pod | loglens
some-command 2>&1 | loglens
loglens < file.log

Wrapper mode (preferred — preserves stderr/stdout separation)

loglens -- kubectl logs -f my-pod
loglens -- go test ./... -v
loglens -- some-command arg1 arg2

Options

--no-follow        Start with follow mode off (default: on)
-x, --exit-on-eof  Auto-exit 5s after EOF when in follow mode
--max-disk <size>  Max disk for offloaded chunks (e.g. 512M, 2G; default: 1G)
--bench <file>     Write timing metrics to <file> for perf testing
-h, --help         Show help

Key bindings

Benchmarking

The cmd/loggen tool emits a ramping log stream at a configurable rate, prefixed with lag-measurement timestamps. Use it with --bench to measure rendering performance:

cd cmd/loggen
go build -o loggen .

# Linear ramp from 100 to 200k lines/sec over 30s:
./loggen --start-rate 100 --end-rate 200000 --duration 30s | loglens --bench out.txt

# Exponential ramp:
./loggen --start-rate 100 --end-rate 500000 --duration 60s --ramp exp | loglens --bench out.txt

# Step function:
./loggen --ramp step --steps 1000,5000,20000,100000 --step-hold 10s | loglens --bench out.txt

# Generate S3-access-log-style JSON lines:
./loggen --shape s3json --start-rate 1000 --end-rate 50000 --duration 20s | loglens

loggen flags: --start-rate, --end-rate, --duration, --ramp (linear|exp|step), --steps, --step-hold, --shape (kuttl|s3json), --shuffle, --no-prefix, --max-lines, --flush-every, --quiet.

Development

make test       # run all tests
make test-race  # run with race detector
make lint       # golangci-lint
make build      # build loglens binary

License

MIT — see LICENSE.