Show HN: Open-source browser for AI agents

Web browsing is continuous and async. Agents think in tools and steps. ABP reformats web navigation into the discrete, multimodal chat format agents know and love.

90.53% on Online Mind2Web — reproducible results

ABP is a Chromium build with MCP + REST baked directly into the browser engine.

• One request = one completed step: settled state + screenshot + event log
• No WebSocket. No CDP session management. Just HTTP.
• ~100ms overhead per action (including screenshots). The bottleneck is the LLM, not the browser.

Try it in 60 seconds (Claude Code)

# 1) Add ABP as an MCP server to Claude Code
claude mcp add browser -- npx -y agent-browser-protocol --mcp

# 2) Sanity check the server is up (optional)
curl -s http://localhost:8222/api/v1/tabs

Wait for the browser to launch and ask Claude:

• “Find me kung pao chicken near 415 Mission St, San Francisco on Doordash.”

What you should notice: every tool call returns a settled page state (screenshot + events), and the page freezes between steps so Claude never races the browser.

AI Agent                                 ABP Chromium
    │                                         │
    │  POST /click (x=450, y=320)             │
    │────────────────────────────────────────>│
    │                                         │  Inject real input event
    │                                         │  Wait for page to settle
    │                                         │  Capture compositor screenshot
    │                                         │  Collect events (tab_created, dialog, file_chooser…)
    │                                         │  Pause JavaScript + virtual time
    │  200 OK: screenshot + events            │
    │<────────────────────────────────────────│
    │
    ·  (agent inspects screenshot, decides)   ·
    │
    │  POST /type (text="Show HN")            │
    │────────────────────────────────────────>│
    │                                         │  Unpause JS + time
    │                                         │  Inject real keyboard events
    │                                         │  Wait for settle → screenshot → events → pause
    │  200 OK: screenshot + events            │
    │<────────────────────────────────────────│

Note: If you have a Playwright MCP server configured, disable it before using ABP to avoid tool name conflicts.

claude mcp add browser -- npx -y agent-browser-protocol --mcp

Then ask Claude: "Go to news.ycombinator.com and find the top post about AI."

codex mcp add browser -- npx -y agent-browser-protocol --mcp

Configure a model with vision and add the MCP server.

{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "browser": {
      "type": "local",
      "command": ["npx", "-y", "agent-browser-protocol", "--mcp"],
      "enabled": true,
      "environment": {
      }
    }
  }
}

Launch ABP:

npx -y agent-browser-protocol

Then point your MCP client at http://localhost:8222/mcp (streamable HTTP).

For example, in Claude Desktop (claude_desktop_config.json):

{
  "mcpServers": {
    "browser": {
      "transport": "streamable-http",
      "url": "http://localhost:8222/mcp"
    }
  }
}

Launch ABP:

npx -y agent-browser-protocol

Then drive it with curl:

# List tabs
curl -s http://localhost:8222/api/v1/tabs

# Navigate (returns screenshot + events)
# Make sure you replace <TAB_ID> with an actual tab_id from above
curl -s -X POST http://localhost:8222/api/v1/tabs/<TAB_ID>/navigate \
  -H 'content-type: application/json' \
  -d '{"url":"https://example.com","screenshot":{"format":"webp"}}'

See docs/REST-API.md for curl examples and the full API reference.

npm package details? See theredsix/abp-npm for the TypeScript SDK, plugin config, and debug server.

Manual binary download? See MANUAL_INSTALL.md for direct download and launch instructions.

Building from source? See COMPILE.md for macOS, Linux, and Windows.

Uninstalling? See Uninstall.

Short demo: Use google maps and find a route from Seattle to LA by train.

Notice the freezing of the spinners while the LLM is thinking. ABP pauses JavaScript and virtual time between actions so the page waits for the agent.

The core problem is a mismatch:

• Web browsing is continuous and asynchronous
• LLM agents reason step-by-step

Most automation stacks force agents to race against a live browser, then patch over the mismatch with waits and retries.

ABP makes browsing a step machine. Each request injects native input, waits for an engine-defined “settled” boundary, captures compositor output (with cursor), returns an event log, then freezes JavaScript + virtual time until the next step.

ABP reformats browsing into a step machine: a request/response contract where the agent only ever acts on a stable, frozen world state.

Each API call is one atomic step. ABP injects real input through Chromium's input system, waits for an engine-defined "settled" boundary, captures compositor output (with cursor), and returns the events that occurred. JavaScript and virtual time freeze between steps. The agent never races against the browser—it observes, decides, acts, and repeats on a world that waits for it.

Docs

• TypeScript SDK + npm details: README
• REST API reference + curl examples: REST-API.md
• Manual binary download + launch: MANUAL_INSTALL.md
• Building from source: COMPILE.md
• Training / SQLite session schema: TRAINING.md

Security notes

• ABP is intended to run locally on your machine.
• The API is served on localhost by default (--abp-port=8222).
• ABP blocks real system input by default; use --allow-system-inputs to override.

ABP embeds an HTTP server directly in the browser process. Requests are routed on the IO thread and dispatched on the UI thread with direct access to Browser, TabStripModel, and the DevTools agent.

+---------------------------------------------------------+
|                  AI Agent (curl / Python / Go)          |
+----------------------------+----------------------------+
                             | REST API
                             v
+---------------------------------------------------------+
|              AbpHttpServer (IO thread)                  |
|              localhost:8222/api/v1/*                    |
+----------------------------+----------------------------+
                             | PostTask
                             v
+---------------------------------------------------------+
|              AbpController (UI thread)                  |
|   Direct access to Browser, TabStripModel, DevTools     |
+----------------------------+----------------------------+
                             |
              +--------------+--------------+
              v              v              v
         +--------+    +----------+    +--------+
         | Input  |    | Renderer |    |Network |
         | System |    |  (Blink) |    | Stack  |
         +--------+    +----------+    +--------+

Every action returns what the agent needs to make the next decision:

{
  "result": {"status": "clicked"},
  "screenshot_before": {
    "data": "base64-webp...",
    "width": 1920, "height": 1080
  },
  "screenshot_after": {
    "data": "base64-webp...",
    "width": 1920, "height": 1080
  },
  "scroll": {"scrollX": 0, "scrollY": 150, "pageWidth": 1280, "pageHeight": 4000, "viewportWidth": 1280, "viewportHeight": 720},
  "events": [
    {"type": "navigation", "virtual_time_ms": 0, "data": {"tab_id": "...", "url": "https://...", "frame_id": "...", "is_main_frame": true}},
    {"type": "dialog", "virtual_time_ms": 0, "data": {"tab_id": "...", "dialog_type": "confirm", "message": "Delete this item?"}},
    {"type": "file_chooser", "virtual_time_ms": 0, "data": {"id": "fc_1", "tab_id": "...", "chooser_type": "open", "multiple": false, "accepts": [".pdf", ".docx"], "pending": true}}
  ],
  "timing": {"action_started_ms": 1700000000000, "action_completed_ms": 1700000000050, "duration_ms": 50},
  "cursor": {"x": 450, "y": 320, "cursor_type": "pointer"}
}

No need to call "take screenshot" after every action. No need to poll for navigation events.

Freeze JavaScript execution between agent actions. The page stops. Timers freeze. Date.now() freezes. When you take a screenshot, you capture a deterministic state.

# Enable execution control
curl -X POST http://localhost:8222/api/v1/tabs/{id}/execution \
  -d '{"paused": true}'

Enabled by default. Disable with --abp-disable-pause.

Request bounding boxes drawn around interactive elements in any action's response screenshot:

# Markup on a click action
curl -X POST http://localhost:8222/api/v1/tabs/{id}/click \
  -d '{"x": 450, "y": 320, "screenshot": {"markup": ["clickable", "typeable"]}}'

# Markup on navigation
curl -X POST http://localhost:8222/api/v1/tabs/{id}/navigate \
  -d '{"url": "https://example.com", "screenshot": {"markup": ["typeable"]}}'

Markup options: clickable, typeable, scrollable, grid, selected.

A compositor-layer cursor that moves with input actions and appears in screenshots. Your agent sees what a human would see.

File choosers, dialogs, and downloads are reported in the event stream:

{
  "events": [
    {"type": "dialog", "data": {"tab_id": "...", "dialog_type": "confirm", "message": "Delete this item?"}}
  ]
}

Handle them with dedicated endpoints:

curl -X POST http://localhost:8222/api/v1/tabs/{id}/dialog/accept

Every action is recorded to a SQLite database with before/after screenshots, parameters, results, timing, and success/failure status. Successful agent sessions become fine-tuning datasets for vision-language models.

Action #1: navigate("https://example.com")
  ├── screenshot_before.webp
  ├── params: {"url": "https://example.com"}
  └── screenshot_after.webp

Action #2: click(450, 320)
  ├── screenshot_before.webp
  ├── params: {"x": 450, "y": 320}
  └── screenshot_after.webp

Control session storage with --abp-session-dir:

./abp --abp-session-dir=./datasets/session-001

See TRAINING.md for the SQLite schema, abp-debug UI, and training pipeline examples.

chrome/browser/abp/                 # Core ABP implementation
  abp_http_server.cc/h              # HTTP server (IO thread)
  abp_controller.cc/h               # Request handling (UI thread)
  abp_action_context.cc/h           # Action lifecycle (pause/resume/screenshot)
  abp_input_dispatcher.cc/h         # Native input dispatch (click/scroll/keys)
  abp_event_observer.cc/h           # CDP event client per tab
  abp_event_collector.cc/h          # Event collection during actions
  abp_mcp_handler.cc/h              # Embedded MCP server (JSON-RPC over HTTP)
  abp_tool_builder.cc/h             # MCP tool schema builder
  abp_history_controller.cc/h       # Session/action history API
  abp_history_database.cc/h         # SQLite history storage
  abp_download_observer.cc/h        # Download tracking
  abp_config.cc/h                   # Runtime configuration
  abp_types.h                       # Shared type definitions
  abp_switches.cc/h                 # Command line flags

plans/                              # Design documents
  API.md                            # REST API specification
  agent-browser-protocol.md         # Architecture
  mcp.md                            # MCP specification

ABP is under active development. Current implementation:

Working:

• Tab management (list, create, close, activate, stop)
• Navigation (URL, back, forward, reload)
• Screenshots with element markup and virtual cursor
• Mouse input (click, move, drag, scroll via native wheel events)
• Keyboard input (type, press, key down/up with modifiers)
• JavaScript execution
• Text extraction (full page or CSS selector)
• Input helpers (slider, clear-text)
• Duration and network wait
• Dialog handling (alert, confirm, prompt, beforeunload)
• File chooser support (local files and base64 content)
• Native select popup handling
• Download management (list, status, cancel, content retrieval)
• Permission prompt handling + geolocation spoofing
• Execution control (JS pause/resume, virtual time)
• History tracking with SQLite (sessions, actions, events)
• Virtual cursor rendering (compositor layer)
• Browser management (status, shutdown)
• Embedded MCP server with 18 tools at /mcp

Not yet implemented:

• Action success/failure tracking
• Recording of human browsing sessions as training data for agent fine-tuning

ABP includes integration tests validating core functionality including navigation, input, screenshots, JavaScript execution, execution control, and MCP protocol compliance.

See TESTING.md for the complete test matrix, test page documentation, and guide for adding new tests.

ABP also exposes a full REST API for direct HTTP integration. See docs/REST-API.md for the quick start and complete endpoint reference.

• Han Wang (@theredsix)

Remove the MCP server from your client:

# Claude Code
claude mcp remove browser

# Codex CLI
codex mcp remove browser

For other clients, delete the browser entry from your MCP configuration file.

ABP is a substantial fork of Chromium. Contributions welcome, please reach out to a maintainer about contributing.

Copyright 2026 Han Wang. All rights reserved.

Chromium is licensed under the BSD 3-Clause License. ABP modifications are Copyright 2026 Han Wang and follow the same license.

ABP builds on the incredible work of the Chromium team. We're grateful for their commitment to open source. This fork was created with the assistance of Claude Code.