kbr (ko-browser)

A simple, fast, token-efficient browser for AI agents — CLI + Go Library.

中文文档 • Quick Start • Agent Notes • Commands • Library • Snapshot Format Spec

ko-browser is a browser automation tool built in Go for AI agents. It exposes the same core model in two forms:

a CLI for shell-driven agent workflows
a Go library for embedding browser control into agent runtimes and tools

Its custom accessibility-tree snapshot format reduces prompt footprint by 46%+ compared with more verbose alternatives.

✨ Key Features

🚀 Single binary — no Node.js, no Playwright runtime needed
🤖 AI-optimized snapshot format — id: role "name" states saves 46%+ tokens
📦 Dual-use — works as a CLI tool AND a Go library (go get)
⚡ Fast startup — ~50ms (Go binary) vs ~500ms (Node.js-based tools)
🔢 Simple element references — click 5
🔍 Optional OCR — Tesseract integration via -tags=ocr build flag for image-heavy pages
🌐 ~86 commands — broad coverage for browser automation workflows

Snapshot Format Comparison

┌─ kbr (46% fewer tokens) ──────────┐  ┌─ verbose snapshot output ──────────┐
│ Page: "Example"                    │  │ - document "Example"               │
│                                    │  │   - navigation "main":             │
│ 1: link "Home"                     │  │     - link "Home" [ref=@e1]        │
│ 2: link "About"                    │  │     - link "About" [ref=@e2]       │
│ 3: textbox "Search" focused        │  │   - search:                        │
│ 4: button "Go"                     │  │     - textbox "Search" [ref=@e3]   │
│                                    │  │     - button "Go" [ref=@e4]        │
└────────────────────────────────────┘  └────────────────────────────────────┘

📖 Read the full Snapshot Format Specification for detailed design decisions, BNF grammar, and examples. (中文版)

📦 Installation

Choose an install path

Use case	Recommended path	Notes
macOS local usage	Homebrew	Installs an OCR-enabled build and pulls in `tesseract`
Linux/macOS manual deployment	GitHub Releases	Download the prebuilt archive and make sure Tesseract runtime libraries are present
Go-based integration or custom builds	From source	Best when embedding `kbr` into your own toolchain

Homebrew

brew tap libi/tap
brew install ko-browser

Homebrew installs kbr with OCR enabled. It pulls in tesseract automatically and builds from source.

Pre-built binaries

Download from GitHub Releases:

Release binaries are also built with OCR enabled. Install Tesseract first so the runtime OCR libraries are available: brew install tesseract on macOS, apt install libtesseract-dev on Linux.

# macOS (Apple Silicon)
curl -LO https://github.com/libi/ko-browser/releases/latest/download/ko-browser-darwin-arm64.tar.gz
tar xzf ko-browser-darwin-arm64.tar.gz
mv kbr /usr/local/bin/kbr

# macOS (Intel)
curl -LO https://github.com/libi/ko-browser/releases/latest/download/ko-browser-darwin-amd64.tar.gz
tar xzf ko-browser-darwin-amd64.tar.gz
mv kbr /usr/local/bin/kbr

# Linux (amd64)
curl -LO https://github.com/libi/ko-browser/releases/latest/download/ko-browser-linux-amd64.tar.gz
tar xzf ko-browser-linux-amd64.tar.gz
mv kbr /usr/local/bin/kbr

From source

# Install kbr with OCR support (requires Tesseract to be installed)
CGO_ENABLED=1 go install -tags=ocr github.com/libi/ko-browser/cmd/kbr@latest

OCR is required for the published packages. This requires Tesseract: brew install tesseract (macOS) / apt install libtesseract-dev (Linux).

Install Chrome (if not already installed)

kbr install              # check & download Chromium
kbr install --with-deps  # also install system dependencies (Linux)

Runtime requirements

Chrome or Chromium is required. Run kbr install if you do not already have a compatible browser.
OCR-enabled builds expect Tesseract runtime libraries on the host.
On Linux CI or sandboxed environments, Chrome may require --no-sandbox-style fallbacks depending on the runner configuration.

🚀 Quick Start

Agent loop

This is the most common shell-driven agent workflow:

kbr open https://example.com
kbr snapshot
kbr click 5
kbr type 8 "hello world"
kbr press Enter
kbr wait load
kbr get text 12

Use snapshot to get the current page structure, act on numeric refs, then re-snapshot after the page changes.

CLI

# Open a page and take a snapshot
kbr open https://www.google.com
kbr snapshot

# Output:
# Page: "Google"
#
# 1: link "Gmail"
# 2: link "Images"
# 3: textbox "Search" focused
# 4: button "Google Search"
# 5: button "I'm Feeling Lucky"

# Interact with elements by ID
kbr click 3
kbr type 3 "ko-browser github"
kbr press Enter

# Take a screenshot
kbr screenshot result.png

# Close the browser
kbr close

Go Library

package main

import (
    "fmt"
    "log"

    "github.com/libi/ko-browser/browser"
)

func main() {
    b, err := browser.New(browser.Options{Headless: true})
    if err != nil {
        log.Fatal(err)
    }
    defer b.Close()

    b.Open("https://www.google.com")

    snap, _ := b.Snapshot()
    fmt.Println(snap.Text)
    // 1: link "Gmail"
    // 2: link "Images"
    // 3: textbox "Search" focused
    // ...

    b.Click(3)
    b.Type(3, "ko-browser github")
    b.Press("Enter")
}

📖 Commands

Common flows

Goal	Commands
Navigate and inspect	`open`, `snapshot`, `get title`, `get url`
Interact with forms	`click`, `type`, `fill`, `select`, `check`, `press`
Wait for state changes	`wait load`, `wait selector`, `wait text`, `wait url`
Debug and verify	`screenshot`, `console messages`, `errors list`, `highlight`
Work with sessions	`tab `, `cookies `, `storage `, `state `

Core Interaction

Command	CLI Usage	Library API
open	`kbr open <url>`	`b.Open(url)`
click	`kbr click <id>`	`b.Click(id)`
dblclick	`kbr dblclick <id>`	`b.DblClick(id)`
type	`kbr type <id> "text"`	`b.Type(id, text)`
fill	`kbr fill <id> "text"`	`b.Fill(id, text)`
press	`kbr press <key>`	`b.Press(key)`
hover	`kbr hover <id>`	`b.Hover(id)`
focus	`kbr focus <id>`	`b.Focus(id)`
check	`kbr check <id>`	`b.Check(id)`
uncheck	`kbr uncheck <id>`	`b.Uncheck(id)`
select	`kbr select <id> "val"`	`b.Select(id, vals...)`
scroll	`kbr scroll down 500`	`b.Scroll("down", 500)`
drag	`kbr drag <src> <dst>`	`b.Drag(srcID, dstID)`
close	`kbr close`	`b.Close()`

Keyboard

kbr press Enter
kbr press Control+a
kbr keyboard type "Hello, World!"
kbr keyboard inserttext "pasted content"

Snapshot & Screenshot

kbr snapshot                     # full accessibility tree
kbr snapshot -i                  # interactive elements only
kbr snapshot -c                  # compact mode
kbr snapshot -d 5                # max depth 5
kbr snapshot -C                  # include cursor elements
kbr snapshot -s "#main"          # scope to CSS selector
kbr snapshot --ocr               # with OCR for images

kbr screenshot out.png           # viewport screenshot
kbr screenshot --full out.png    # full page
kbr screenshot --annotate out.png # annotated with element IDs

Navigation

kbr back
kbr forward
kbr reload

Get Information

kbr get title                    # page title
kbr get url                      # current URL
kbr get text <id>                # element inner text
kbr get html <id>                # element innerHTML
kbr get value <id>               # input value
kbr get attr <id> href           # element attribute
kbr get count ".item"            # count matching elements
kbr get box <id>                 # bounding box
kbr get styles <id>              # computed styles
kbr get cdp-url                  # CDP WebSocket URL

Check State

kbr is visible <id>              # → true/false
kbr is enabled <id>
kbr is checked <id>

Find Elements

kbr find role button --name Submit
kbr find text "Sign In"
kbr find label "Email"
kbr find placeholder "Search..."
kbr find alt "Logo"
kbr find title "tooltip"
kbr find testid "login-form"
kbr find first ".card"
kbr find last ".card"
kbr find nth 2 ".card"
# Add --exact for exact text matching
kbr find text "Sign In" --exact

Wait

kbr wait time 2s                 # wait 2 seconds
kbr wait selector "#loading"     # wait for element
kbr wait url "**/dashboard"      # wait for URL match
kbr wait load                    # wait for networkidle
kbr wait text "Welcome"          # wait for text
kbr wait fn "window.ready"       # wait for JS expression
kbr wait hidden "#spinner"       # wait for element to hide
kbr wait download ./file.pdf     # wait for download

Mouse (Low-level)

kbr mouse move 100 200
kbr mouse click 100 200
kbr mouse down 100 200
kbr mouse up 100 200
kbr mouse wheel 100 200 0 300    # x y deltaX deltaY

Tabs

kbr tab list
kbr tab new https://example.com
kbr tab switch 2
kbr tab close 1

Network

kbr network route "**/api/*" --action block
kbr network unroute "**/api/*"
kbr network requests
kbr network start-logging
kbr network clear

Storage & Cookies

kbr cookies get
kbr cookies set session_id "abc123" --domain example.com
kbr cookies delete session_id
kbr cookies clear

kbr storage get theme --type local
kbr storage set theme "dark" --type local
kbr storage delete theme --type local
kbr storage clear --type local
kbr storage list --type session

Browser Settings

kbr set viewport 1920 1080
kbr set viewport 1920 1080 2     # with 2x scale
kbr set device "iPhone 12"
kbr set geo 37.7749 -122.4194
kbr set offline true
kbr set headers '{"X-Custom":"value"}'
kbr set credentials admin secret
kbr set media dark
kbr set colorscheme dark

File Operations

kbr upload <id> ./document.pdf
kbr download <id> ./output/

JavaScript Evaluation

kbr eval "document.title"
kbr eval -b "ZG9jdW1lbnQudGl0bGU="   # base64 encoded
cat script.js | kbr eval --stdin

Diff

kbr diff snapshot                              # compare with last snapshot
kbr diff snapshot --baseline before.txt
kbr diff screenshot --baseline before.png
kbr diff url https://v1.example.com https://v2.example.com

Debug & Clipboard

kbr console messages
kbr console clear
kbr errors list
kbr highlight <id>
kbr inspect                      # open DevTools

kbr clipboard read
kbr clipboard write "text"
kbr clipboard copy               # Ctrl+C
kbr clipboard paste              # Ctrl+V

Trace & Record

kbr trace start
kbr trace stop ./trace.zip

kbr profiler start
kbr profiler stop ./profile.json

kbr record start ./recording
kbr record stop

Auth

kbr auth save github --url https://github.com/login --username user --password pass
kbr auth login github
kbr auth list
kbr auth show github
kbr auth delete github

Session Management

kbr session                      # show current session
kbr session list                 # list all active sessions
kbr --session test open example.com  # use named session

Selector Syntax

kbr supports three selector formats, auto-detected:

Input	Type	Example
Number	Snapshot ID	`kbr click 5`
CSS	CSS Selector	`kbr click "#submit"`
XPath	XPath	`kbr click "//button[@type='submit']"`

🔧 Global Options

Flag	Description
`--session <name>`	Isolated session name (default: "default")
`--headed`	Show browser window
`--json`	JSON output
`--timeout <duration>`	Operation timeout (default: 30s)
`--profile <path>`	Persistent Chrome user data directory
`--state <path>`	Load saved browser state (cookies + localStorage)
`--config <path>`	Config file path
`--user-agent <ua>`	Custom User-Agent
`--proxy <url>`	Proxy server URL
`--proxy-bypass <hosts>`	Hosts to bypass proxy
`--ignore-https-errors`	Ignore HTTPS certificate errors
`--allow-file-access`	Allow file:// URLs
`--extension <path>`	Load Chrome extension (repeatable)
`--args <args>`	Extra Chrome arguments
`--download-path <path>`	Default download directory
`--screenshot-dir <path>`	Default screenshot output directory
`--screenshot-format <fmt>`	Screenshot format: png, jpeg
`--content-boundaries`	Wrap output with boundary markers
`--debug`	Debug output

📚 Library API

Installation

go get github.com/libi/ko-browser@latest

Quick Example

package main

import (
    "fmt"
    "time"

    "github.com/libi/ko-browser/browser"
)

func main() {
    b, _ := browser.New(browser.Options{
        Headless: true,
        Timeout:  30 * time.Second,
    })
    defer b.Close()

    // Navigate
    b.Open("https://www.baidu.com")

    // Snapshot → interact
    snap, _ := b.Snapshot()
    fmt.Println(snap.Text)
    // Page: "百度一下，你就知道"
    //
    // 1: link "新闻"
    // 2: link "hao123"
    // 3: textbox "搜索" focused
    // 4: button "百度一下"

    b.Click(3)
    b.Type(3, "hello world")
    b.Press("Enter")

    // Wait & screenshot
    b.WaitLoad()
    b.Screenshot("result.png")
}

Advanced: Direct AX Tree Access

import (
    "github.com/libi/ko-browser/axtree"
    "github.com/libi/ko-browser/browser"
    "github.com/libi/ko-browser/ocr"
)

b, _ := browser.New(browser.Options{Headless: true})
defer b.Close()
b.Open("https://example.com")

// Low-level AX Tree API
rawNodes, _ := axtree.Extract(b.Context())
tree := axtree.BuildAndFilter(rawNodes)
text := axtree.Format(tree)
idMap := axtree.BuildIDMap(tree)

// Snapshot with OCR
snap, _ := b.Snapshot(browser.SnapshotOptions{
    EnableOCR:    true,
    OCRLanguages: []string{"eng", "chi_sim"},
})

Connect to Existing Browser

// Connect via CDP WebSocket
b, _ := browser.Connect("ws://localhost:9222/devtools/browser/...", browser.Options{})
defer b.Close()

snap, _ := b.Snapshot()
fmt.Println(snap.Text)

Full API Reference

Click to expand all Browser methods

Navigation

Open(url string) error
Back() error
Forward() error
Reload() error

Snapshot

Snapshot(opts ...SnapshotOptions) (*SnapshotResult, error)

Interaction

Click(id int) error
ClickNewTab(id int) error
DblClick(id int) error
Type(id int, text string) error
Fill(id int, text string) error
Press(key string) error
KeyboardType(text string) error
KeyboardInsertText(text string) error
Hover(id int) error
Focus(id int) error
Check(id int) error
Uncheck(id int) error
Select(id int, values ...string) error
Scroll(direction string, pixels int) error
ScrollIntoView(id int) error

Mouse

MouseMove(x, y float64) error
MouseClick(x, y float64, opts ...MouseOptions) error
MouseDown(x, y float64, opts ...MouseOptions) error
MouseUp(x, y float64, opts ...MouseOptions) error
MouseWheel(x, y, deltaX, deltaY float64) error
Drag(srcID, dstID int) error
DragCoords(srcX, srcY, dstX, dstY float64) error

Query

GetTitle() (string, error)
GetURL() (string, error)
GetText(id int) (string, error)
GetHTML(id int) (string, error)
GetValue(id int) (string, error)
GetAttr(id int, name string) (string, error)
GetCount(cssSelector string) (int, error)
GetBox(id int) (*BoxResult, error)
GetStyles(id int) (string, error)
GetCDPURL() (string, error)

State

IsVisible(id int) (bool, error)
IsEnabled(id int) (bool, error)
IsChecked(id int) (bool, error)

Find

FindRole(role, name string, opts ...FindOption) (*FindResults, error)
FindText(text string, opts ...FindOption) (*FindResults, error)
FindLabel(label string, opts ...FindOption) (*FindResults, error)
FindPlaceholder(text string, opts ...FindOption) (*FindResults, error)
FindAlt(text string, opts ...FindOption) (*FindResults, error)
FindTitle(text string, opts ...FindOption) (*FindResults, error)
FindTestID(testID string) (*FindResults, error)
FindFirst(css string) (*FindResults, error)
FindLast(css string) (*FindResults, error)
FindNth(css string, n int) (*FindResults, error)

Wait

Wait(d time.Duration) error
WaitSelector(css string, timeout ...time.Duration) error
WaitURL(pattern string, timeout ...time.Duration) error
WaitLoad(timeout ...time.Duration) error
WaitText(text string, timeout ...time.Duration) error
WaitFunc(expression string, timeout ...time.Duration) error
WaitHidden(css string, timeout ...time.Duration) error
WaitDownload(savePath string, timeout ...time.Duration) (string, error)

Screenshot & PDF

Screenshot(path string, opts ...ScreenshotOptions) error
ScreenshotToBytes(opts ...ScreenshotOptions) ([]byte, error)
ScreenshotAnnotated(path string, opts ...ScreenshotOptions) error
PDF(path string, opts ...PDFOptions) error

Eval

Eval(expression string) (string, error)

File

Upload(id int, files ...string) error
UploadCSS(css string, files ...string) error
Download(id int, saveDir string, opts ...DownloadOptions) (string, error)

Tabs

TabList() ([]TabInfo, error)
TabNew(url string) error
TabClose(index int) error
TabSwitch(index int) error

Network

NetworkRoute(pattern string, action RouteAction) error
NetworkUnroute(pattern string) error
NetworkRequests() ([]NetworkRequest, error)
NetworkStartLogging() error
NetworkClearRequests()

Storage & Cookies

CookiesGet() ([]CookieInfo, error)
CookieSet(cookie CookieInfo) error
CookieDelete(name string) error
CookiesClear() error
StorageGet(storageType, key string) (string, error)
StorageSet(storageType, key, value string) error
StorageDelete(storageType, key string) error
StorageClear(storageType string) error
StorageGetAll(storageType string) (map[string]string, error)

Settings

SetViewport(width, height int, scale ...float64) error
SetDevice(name string) error
SetGeo(lat, lon float64) error
ClearGeo() error
SetOffline(offline bool) error
SetHeaders(headers map[string]string) error
SetCredentials(user, pass string) error
SetMedia(features ...MediaFeature) error
SetColorScheme(scheme string) error

Debug

ConsoleStart() error
ConsoleMessages() ([]ConsoleMessage, error)
ConsoleMessagesByLevel(level string) ([]ConsoleMessage, error)
ConsoleClear()
PageErrors() ([]PageError, error)
PageErrorsClear()
Highlight(id int) error
OpenDevTools() error

Clipboard

ClipboardRead() (string, error)
ClipboardWrite(text string) error
ClipboardCopy() error
ClipboardPaste() error

Diff

DiffSnapshot(opts ...DiffSnapshotOptions) (*DiffSnapshotResult, error)
DiffScreenshot(opts DiffScreenshotOptions) (*DiffScreenshotResult, error)
DiffURL(url1, url2 string, opts ...DiffURLOptions) (*DiffURLResult, error)

Trace & Record

TraceStart(categories ...string) error
TraceStop(outputPath string) error
ProfilerStart() error
ProfilerStop(outputPath string) error
RecordStart(outputPath string) error
RecordStop() (int, error)

State

ExportState(outputPath string) error
ImportState(inputPath string) error
ApplyState(state *BrowserState) error

⚙️ Configuration

kbr loads configuration in this priority (low → high):

~/.ko-browser/config.json — user-level defaults
./ko-browser.json — project-level overrides
Environment variables (KO_BROWSER_*)
CLI flags — override everything

{
  "headed": true,
  "proxy": "http://localhost:8080",
  "profile": "./browser-data",
  "screenshotFormat": "jpeg",
  "downloadPath": "./downloads"
}

🏗️ Architecture

kbr
├── cmd/kbr/      ★ CLI entry point — `go install .../cmd/kbr@latest`
├── browser/      ★ Public Go library — core browser API
├── axtree/       ★ Public — AX Tree extraction, filtering, formatting
├── selector/     ★ Public — element selector parsing (ID/CSS/XPath)
├── ocr/          ★ Public — Tesseract OCR engine (build tag: ocr)
├── cmd/            CLI — cobra command definitions
└── internal/       CLI-only — daemon, session management

The browser/, axtree/, selector/, and ocr/ packages are all public and importable via go get. The internal/ package is only used by the CLI daemon. OCR requires -tags=ocr at build time.

Agent Notes

If you are an agent reading this README, use kbr as an interactive browser with a compact text interface.

Prefer kbr snapshot as the primary page representation. It is the most token-efficient output and gives stable numeric refs.
Use numeric refs like kbr click 5, kbr type 8 "hello", and kbr get text 12 after taking a fresh snapshot.
Re-snapshot after navigation or DOM mutations. Element IDs are snapshot-local, not permanent selectors.
Use kbr get, kbr find, and kbr wait for targeted reads instead of repeatedly taking full screenshots.
Use OCR only when the page content is image-heavy or inaccessible through the DOM/accessibility tree.
Prefer CSS/XPath selectors only when you already know the target precisely or when numeric refs are unavailable.
The published Homebrew package and release binaries are built with OCR enabled, so Tesseract runtime libraries are expected on the host.

Install as an agent skill

If your agent framework supports local skills, install kbr first, then copy the repository skill directory into your agent's skills directory as ko-browser/.

<agent-skills-dir>/
  ko-browser/
    SKILL.md

The source skill lives here:

skills/ko-browser/SKILL.md

Example:

mkdir -p <agent-skills-dir>/ko-browser
cp skills/ko-browser/SKILL.md <agent-skills-dir>/ko-browser/SKILL.md

After that, make sure the kbr binary is available in the agent runtime PATH. For agent hosts that also support executable-tool registration, you can expose kbr directly in addition to the skill file.

🤝 Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

git clone https://github.com/libi/ko-browser.git
cd ko-browser
go build -o kbr ./cmd/kbr/              # without OCR
go build -tags=ocr -o kbr ./cmd/kbr/     # with OCR
go test ./tests/ -v -timeout 180s

📄 License

MIT

Name		Name	Last commit message	Last commit date
Latest commit History 17 Commits
.github/workflows		.github/workflows
axtree		axtree
browser		browser
cmd		cmd
docs		docs
examples		examples
internal		internal
ocr		ocr
scripts		scripts
selector		selector
skills/ko-browser		skills/ko-browser
testdata		testdata
tests		tests
.gitignore		.gitignore
LICENSE		LICENSE
README-CN.md		README-CN.md
README.md		README.md
go.mod		go.mod
go.sum		go.sum

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kbr (ko-browser)

✨ Key Features

Snapshot Format Comparison

📦 Installation

Choose an install path

Homebrew

Pre-built binaries

From source

Install Chrome (if not already installed)

Runtime requirements

🚀 Quick Start

Agent loop

CLI

Go Library

📖 Commands

Common flows

Core Interaction

Keyboard

Snapshot & Screenshot

Navigation

Get Information

Check State

Find Elements

Wait

Mouse (Low-level)

Tabs

Network

Storage & Cookies

Browser Settings

File Operations

JavaScript Evaluation

Diff

Debug & Clipboard

Trace & Record

Auth

Session Management

Selector Syntax

🔧 Global Options

📚 Library API

Installation

Quick Example

Advanced: Direct AX Tree Access

Connect to Existing Browser

Full API Reference

⚙️ Configuration

🏗️ Architecture

Agent Notes

Install as an agent skill

🤝 Contributing

📄 License

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