Exploring OpenClaw Browser Control and Canvas Features

Two Hidden Features in the Boot Log

If you’ve been reading your OpenClaw gateway logs carefully, you’ve noticed two lines that appear on every startup but are easy to overlook:

2026-02-25T23:38:09.648Z [canvas] host mounted at
  http://0.0.0.0:18789/__openclaw__/canvas/ (root /home/node/.openclaw/canvas)

2026-02-25T23:38:09.864Z [browser/server] Browser control listening on
  http://127.0.0.1:18791/ (auth=token)

These are two distinct features that extend OpenClaw well beyond a simple chat relay.

The Canvas Host

What It Is

The Canvas is a file-hosting endpoint built directly into the gateway. It serves static files from the agent’s canvas directory at /__openclaw__/canvas/ on the gateway’s main port (18789).

Where Files Live

Inside the container:

docker exec -it openclaw-openclaw-gateway-1 sh -lc \
  'ls -la /home/node/.openclaw/canvas'

total 8
drwxr-xr-x  2 node node 4096 Feb 25 23:02 .
drwxrwxr-x 11 node node 4096 Feb 25 23:36 ..

On the host (through the volume mount):

ls -la ~/.openclaw/canvas/

How the Agent Uses It

When the agent generates visual output — charts, diagrams, HTML reports — it writes files to the canvas directory. These files are immediately accessible via HTTP:

http://<your-vm-ip>:18789/__openclaw__/canvas/report.html
http://<your-vm-ip>:18789/__openclaw__/canvas/chart.png

This means the agent can generate a visualization and share a direct link in a chat message — no separate file-hosting service needed.

Canvas Use Cases

Accessing the Canvas

From your local machine (via SSH tunnel):

ssh -L 18789:localhost:18789 azureuser@<vm-ip>
# Then open: http://localhost:18789/__openclaw__/canvas/

Or directly if port 18789 is open in your NSG:

http://<vm-public-ip>:18789/__openclaw__/canvas/

The Browser Control Server

What It Is

OpenClaw includes a built-in headless Chromium browser that the agent can control programmatically. The browser control server listens on a separate port:

[browser/server] Browser control listening on
  http://127.0.0.1:18791/ (auth=token)

Key details from the log:

Why 127.0.0.1?

The browser control server binds to localhost only — it’s not accessible from outside the container. This is a security measure. The browser has full rendering capabilities and can access the internet, so exposing its control interface would be dangerous.

Only the gateway process (running in the same container) can communicate with the browser server.

What the Agent Can Do

With browser control, the agent can:

• Browse web pages — Research information, read documentation
• Take screenshots — Capture visual evidence of web pages
• Fill forms — Interact with web applications
• Extract data — Scrape structured data from websites
• Generate PDFs — Render pages to PDF format

CLI Commands

OpenClaw provides CLI commands to manage the browser:

# Browser management
docker compose run --rm openclaw-cli browser --help

From the CLI help output:

browser *    Manage OpenClaw's dedicated browser (Chrome/Chromium)

Port Relationship

The three OpenClaw ports form a clear architecture:

In dev mode (--dev), these shift to 19001, 19002, and 19003 respectively.

Configuring the Browser

Resource Limits

On an Azure B2s (2 vCPU, 4 GB RAM), Chromium can be memory-hungry. Configure resource limits in your Docker Compose file:

services:
  openclaw-gateway:
    deploy:
      resources:
        limits:
          memory: 2G  # Cap total container memory
    environment:
      - CHROMIUM_FLAGS=--disable-gpu --no-sandbox --disable-dev-shm-usage

Disabling the Browser

If you don’t need browser capabilities, you can reduce memory usage by disabling it:

docker compose run --rm openclaw-cli config set browser.enabled false
docker compose restart openclaw-gateway

Check the startup logs — the [browser/server] line should no longer appear.

Browser Data Persistence

Browser data (cookies, local storage) lives inside the container. If you need persistent browser state across restarts, ensure the browser data directory is volume-mounted.

Canvas Directory Structure

As the agent uses the system, the canvas directory populates:

~/.openclaw/canvas/
├── index.html          # Auto-generated index (if enabled)
├── reports/
│   ├── daily-2026-02-25.html
│   └── weekly-summary.html
├── charts/
│   └── memory-usage.svg
└── exports/
    └── conversation-log.pdf

Keeping Canvas Clean

The canvas directory grows over time. Add a cleanup cron job:

# Remove canvas files older than 7 days
find ~/.openclaw/canvas/ -type f -mtime +7 -delete

Or use OpenClaw’s built-in cron:

docker compose run --rm openclaw-cli cron --help

Security Implications

Canvas Access Control

The canvas endpoint inherits the gateway’s security settings. If dangerouslyAllowHostHeaderOriginFallback is enabled, anyone who can reach port 18789 can access canvas files:

[gateway] security warning: dangerous config flags enabled:
  gateway.controlUi.dangerouslyAllowHostHeaderOriginFallback=true

In production, either:

1. Restrict with NSG rules — limit port 18789 to trusted IPs
2. Use SSH tunnels — access canvas only through tunneled connections
3. Set up a reverse proxy — add authentication at the proxy layer

Browser Isolation

The browser server’s 127.0.0.1 bind is the primary security boundary. But the agent can still use the browser to:

• Access internal network resources (if the container has network access)
• Make outbound HTTP requests to any site
• Store cookies and session data

Monitor browser activity through the gateway logs:

docker logs --tail=200 openclaw-openclaw-gateway-1 | grep "\[browser"

Verifying Both Features

Canvas Check

# Confirm canvas is mounted
docker logs openclaw-openclaw-gateway-1 | grep "\[canvas\]"

# Expected output:
# [canvas] host mounted at http://0.0.0.0:18789/__openclaw__/canvas/
#   (root /home/node/.openclaw/canvas)

# List canvas files
docker exec -it openclaw-openclaw-gateway-1 sh -lc \
  'ls -la /home/node/.openclaw/canvas/'

Browser Check

# Confirm browser server is running
docker logs openclaw-openclaw-gateway-1 | grep "\[browser"

# Expected output:
# [browser/server] Browser control listening on
#   http://127.0.0.1:18791/ (auth=token)

# Test connectivity from inside the container
docker exec -it openclaw-openclaw-gateway-1 sh -c \
  'wget -qO- http://127.0.0.1:18791/health 2>/dev/null || echo "check auth"'

Series Navigation

Previous: OpenClaw Agent Tool Execution Errors and Sandbox Permissions Next: OpenClaw Gmail Watcher and Email Channel Integration

Part 28 of the OpenClaw on Azure series. Your agent now has eyes (browser) and a gallery wall (canvas) — it’s not just chatting anymore.