# Agent Browser

> Open a URL in the headless agent-browser, with a preflight health check. Verifies agent-browser is installed and Chromium launches before navigating. Errors out with a diagnostic trace if anything fails. TRIGGER when: asked to open a page, browse a URL, take a screenshot, or test a site with agent-browser.

- Skill: `mifunedev/agent-browser` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add mifunedev/agent-browser`
- Raw SKILL.md: https://api.skillmd.com/api/skills/mifunedev/agent-browser/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: mifunedev (https://skillmd.com/u/mifunedev)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/mifunedev/agent-browser

---


# Agent Browser

Open a URL in the headless browser. Runs a health check first — if the browser is broken, errors out with a full diagnostic trace so the user can fix it.

## Instructions

### Step 1 — Parse arguments

Arguments received: `$ARGUMENTS`

- **URL**: `$0` (required)
- **VIEWPORT**: value after `--viewport` flag if present. Default: `desktop`
- **SESSION**: value after `--session` flag if present (optional, for session isolation)

If URL is missing, ask the user to provide it.

### Viewport defaults

| Name | Width | Height |
|------|-------|--------|
| `desktop` | 1920 | 1080 |
| `mobile` | 414 | 896 |

Default is `desktop` if `--viewport` is not specified.

### Step 2 — Preflight health check

Run each check sequentially. If any check fails, **stop immediately** and report the full diagnostic trace to the user.

#### 2a. Check agent-browser is installed

```bash
command -v agent-browser && agent-browser --version 2>&1 || echo "FAIL: agent-browser not found in PATH"
```

If not found, install it — **use npm (not pnpm)** and **pin to 0.8.5**:

```bash
sudo npm install -g agent-browser@0.8.5
```

Then install Chromium + system deps. `agent-browser install --with-deps`
shells out to a `playwright` binary that isn't bundled with this package,
so on a fresh image you'll also need the playwright CLI available:

```bash
agent-browser install --with-deps    # installs system libs (apt)
# If it ends with "sh: 1: playwright: not found":
sudo npm install -g playwright@latest
npx playwright install chromium
```

Verify:

```bash
agent-browser --version     # → agent-browser 0.8.5
agent-browser open about:blank && agent-browser close
```

Rationale for the pins:
- **npm, not pnpm** — `PNPM_HOME` is `/usr/local/share/pnpm`, owned by
  root; `pnpm add -g` as the sandbox user fails with `EACCES`.
- **0.8.5** — later majors have breaking CLI changes; the rest of this
  skill targets 0.8.5's flags.

Or rebuild the image with `INSTALL_AGENT_BROWSER=true` in
`.devcontainer/.env` to bake this in.

After installing, resume the health check from step 2b — **do not stop**.

#### 2b. Check Chromium launches

```bash
agent-browser open "about:blank" 2>&1
```

If this fails (non-zero exit, error output mentioning "chrome", "chromium", "ENOENT", "launch", or "sandbox"), report the full error and:

```
Chromium failed to launch. Common causes:

1. Missing system dependencies:
   apt-get install -y libnss3 libatk1.0-0 libatk-bridge2.0-0 libcups2 \
     libdrm2 libxkbcommon0 libxcomposite1 libxdamage1 libxrandr2 libgbm1 \
     libpango-1.0-0 libcairo2 libasound2 libxshmfence1 libx11-xcb1 \
     fonts-liberation xdg-utils

2. Chromium not downloaded:
   agent-browser install --with-deps

3. Sandbox permission issue (containers):
   Ensure --no-sandbox is set or container has SYS_ADMIN capability.
```

**Stop here** — do not continue. Close the failed session first:

```bash
agent-browser close 2>/dev/null
```

#### 2c. Verify page loaded

```bash
agent-browser snapshot -c 2>&1
```

If snapshot returns content (even minimal), the browser is healthy. Close the health-check session:

```bash
agent-browser close
```

### Step 2d — DNS resolution check (tunnel hostnames)

If the URL contains a hostname served by a tunnel or reverse proxy, the container's DNS may not resolve it yet. Check and fix:

```bash
HOSTNAME=$(echo "$URL" | sed 's|https\?://||; s|/.*||; s|:.*||')
if ! getent hosts "$HOSTNAME" &>/dev/null; then
  # Resolve via Cloudflare DNS API
  IP=$(curl -sf "https://cloudflare-dns.com/dns-query?name=${HOSTNAME}&type=A" \
    -H "accept: application/dns-json" | python3 -c "import sys,json; d=json.load(sys.stdin); print(d['Answer'][0]['data'])" 2>/dev/null)
  if [ -n "$IP" ]; then
    echo "$IP $HOSTNAME" | sudo tee -a /etc/hosts >/dev/null
    echo "Added $HOSTNAME -> $IP to /etc/hosts (container DNS didn't resolve it)"
  else
    echo "FAIL: $HOSTNAME does not resolve. Check tunnel/DNS routing."
    # Stop here
  fi
fi
```

This ensures agent-browser can reach tunnel-served sites even when the container's DNS resolver hasn't propagated the CNAME yet.

### Step 3 — Open the target URL with viewport

Set the viewport size based on the selected viewport, then open the URL:

```bash
# Desktop: 1920x1080, Mobile: 375x812
agent-browser open "$URL" --viewport-width $WIDTH --viewport-height $HEIGHT $( [ -n "$SESSION" ] && echo "--session $SESSION" )
```

If `agent-browser open` does not support `--viewport-width`/`--viewport-height` flags, open the URL first, then resize:

```bash
agent-browser open "$URL" $( [ -n "$SESSION" ] && echo "--session $SESSION" )
agent-browser execute "await page.setViewportSize({ width: $WIDTH, height: $HEIGHT })"
```

If this fails, report the error with the full output.

### Step 4 — Confirm page loaded and screenshot

```bash
agent-browser snapshot -c
```

Report a summary of what loaded (page title, key elements visible).

Take a screenshot to `.claude/screenshots/` using a descriptive filename derived from the URL path:

```bash
# Generate filename from URL: strip protocol, replace / with --, remove trailing -
FILENAME=$(echo "$URL" | sed 's|https\?://||; s|/|--|g; s|--$||; s|[^a-zA-Z0-9._-]|-|g')
agent-browser screenshot ".claude/screenshots/${FILENAME}.png"
```

Example: `https://my-app.oh-local.localhost:8443/guide/configuration/` → `.claude/screenshots/my-app.oh-local.localhost-8443--guide--configuration.png`

### Step 5 — Report

```
Browser ready.

  URL:        $URL
  Viewport:   $VIEWPORT ($WIDTHx$HEIGHT)
  Session:    $SESSION (or "default")
  Screenshot: .claude/screenshots/$FILENAME.png

  Next steps:
    agent-browser screenshot <path>       # capture to custom path
    agent-browser snapshot -i             # interactive elements
    agent-browser is visible "<selector>" # wait for element
    agent-browser close                   # end session (always do this)
```

## Session Hygiene

- ALWAYS close browser sessions when done: `agent-browser close`
- Use `--session <name>` for isolation between concurrent test runs
- If any step errors, close the session before reporting to the user