tess

A less-style terminal pager for files, pipes, and live logs — with first-class support for structured-log filtering, pretty-printing of JSON/YAML/TOML/XML/HTML/CSV, ANSI color passthrough for piped tools that emit colored output, wrap-aware scrolling of long lines, multi-file navigation with :n/:p/:e colon commands, and ctags/etags tag jumping (-t NAME, Ctrl-]/Ctrl-T). Escape to the shell with !cmd, preprocess inputs ($LESSOPEN / --preprocess), and remap keys via ~/.config/tess/keys.toml. Written in Rust. macOS + Linux.

tess /var/log/syslog                                # like `less`, but newer keys
git log | tess                                      # pipe-friendly
tess -f --tail 1000 huge.log                        # tail -f the last 1000 lines
tess --format apache-combined --filter status~^5 access.log
tess --prettify config.json                         # auto-detected JSON layout

Why?

less is great, but it doesn't know what your data is. tess adds a small amount of structure-awareness without trying to be a log explorer:

• Parse-aware filtering. Declare a log format once (built-in or your own regex), then keep only the lines whose parsed status, ip, level, etc. match a predicate. Hide them entirely or just dim them so context is preserved.
• Multi-line records. Set record_start in formats.toml (or pass --record-start REGEX) to group continuation lines under their leading record — search, filter, and --grep then operate on whole records like PHP stack traces or Java exception dumps.
• Pretty-printing. Open a JSON / YAML / TOML / XML / HTML / CSV file and see it laid out, not minified — without leaving the pager. Toggle on/off with Shift-P.
• Live + follow modes. --follow for tail-style appended logs (background reader thread, doesn't fight your tty); --live for whole-file rewrites (editor saves, AI agents, build outputs).
• Cheap on huge files. mmap'd file source, lazy line indexing, --tail N reverse-scans only as far as needed.
• Long-line scrolling that actually works. j walks wrap-rows so the last 1000 chars of a 5000-char line are reachable; J / K jump by whole logical lines when you don't want to scroll through every wrap.

It is not a log search/correlation tool, structured query engine, or replacement for lnav. It's a single-file pager.

Install

Homebrew (macOS / Linuxbrew)

brew install codedeviate/cli/tess

The formula lives in the codedeviate/homebrew-cli tap and builds from source on first install.

crates.io

cargo install tess-cli

The crate is published as tess-cli because the bare tess name was already taken (an unrelated parked crate). The installed binary is still tess.

From source

tar -xzf tess-<version>.tar.gz
cd <extracted-dir>
cargo build --release
install -m 755 target/release/tess ~/.local/bin/tess

Requires Rust 1.85+. See INSTALL.md for full instructions, including a macOS 26 (Tahoe) gotcha where cp into /usr/local/bin can get a binary SIGKILLed by the kernel — install avoids it.

Quick start

Run tess --examples for a curated list, or tess --manual for the full manual paged through tess itself.

Key bindings

Vim-ish + less-ish hybrid. The full table is in MANUAL.md; these are the ones you'll use:

Pressing /<Enter> (or ?<Enter>) with an empty pattern repeats the last search in the typed direction, the way less does it.

Plain-text grep

If you don't have (or don't need) a parsed format, --grep PATTERN filters by regex against the raw line. Repeatable, AND-combined.

tess --grep error app.log
tess --grep error --grep '^\[' app.log    # both patterns must match
tess --grep error --dim app.log           # show all, dim non-matches

--grep composes with --filter when both are set (line must match both):

tess --format apache-combined --filter status=500 --grep timeout access.log

Structured log filtering

Three formats ship built-in: apache-common, apache-combined, nginx-combined. Drop a TOML file at ~/.config/tess/formats.toml to define your own:

[format.app]
pattern = '^(?P<ts>\S+) (?P<level>\w+) (?P<msg>.+)$'

Then:

tess --format app --filter 'level!=DEBUG' app.log         # hide DEBUG lines
tess --format app --filter 'level=ERROR' --dim app.log    # keep DEBUG dimmed for context

Operators: = (exact), != (exact ≠), ~ (regex), !~ (regex ≠). Multiple --filter flags AND together. Quote arguments with '…' in interactive shells so ! doesn't trigger history expansion.

Run tess --list-formats to see what's available, including your custom ones.

Status line

<source>  <top>-<bottom>/<total>  <pct>%  +<wrap>/<wraps>  [<format>]  [filter|dim]  [/<search>]  [pretty:<type>]  (L)  (F)

Each segment appears only when relevant. The +12/50 indicator surfaces wrap-row position when scrolled inside a long wrapping line, so j is visibly making progress.

Images

tess auto-detects image files by magic bytes (PNG, JPEG, GIF, BMP, WebP, TIFF, TGA, ICO, PNM) and renders them as colored ASCII art directly in the pager. No flags needed — just open the file:

tess photo.png                                # colored ASCII art in the pager
tess logo.gif                                 # GIFs render their first frame
tess --blocks --image-width 100 photo.png     # higher-detail half-block render
tess photo.png -o art.txt                     # save the art (ANSI color) to a file
tess photo.png --no-color --stdout > art.txt  # plain, portable text

Flags:

Color output uses 24-bit truecolor SGR; pass --no-color for a plain character-only render. Export the art with -o FILE or --stdout — ANSI-colored by default, plain text under --no-color.

The image feature is on by default. Build without it (--no-default-features) for a smaller binary that treats all inputs as text.

Command-line flags

The full set, alphabetical by long name — the same order tess --help lists them. Run tess --manual for the long-form descriptions.

Project status

Pre-1.0; the CLI is settling but small breakage at minor-version boundaries is permitted (and called out in commit messages). Daily-driver-quality on macOS and Linux. No Windows support — the stdin / /dev/tty plumbing is Unix-specific.

Architecture notes and module layout: CLAUDE.md. Deferred features and intentional non-goals: OUT-OF-SCOPE.md.

Building from source

cargo build --release                  # binary at target/release/tess
cargo test -- --test-threads=1         # unit + integration tests (PTY tests need serial)
cargo bench                            # criterion baselines (HTML in target/criterion/)
cargo run -- Cargo.toml                # quick interactive run
ls -la | cargo run --release           # piped stdin

License

MIT — see LICENSE.