opencode-browser-mcp

One shared browser profile with separate tab ownership for every OpenCode session. The plugin wraps chrome-devtools-mcp and routes each conversation through its own browser tabs while sharing cookies, logins, local storage, cache, and extensions.

Requirements

• OpenCode 1.18 or newer
• Linux x64
• Bun
• A local Chromium-family browser
• A graphical session, unless OPENCODE_BROWSER_HEADLESS=true

Setup

Add the plugin to opencode.json:

{
  "$schema": "https://opencode.ai/config.json",
  "plugin": ["@mirsella/opencode-browser-mcp"]
}

Restart OpenCode after changing its configuration. That is the complete setup. You do not need a separate installation, broker command, or background service.

The first OpenCode adapter starts the packaged native broker automatically. Concurrent OpenCode instances converge on the same private socket and browser profile. The broker remains available while at least one adapter is connected, then closes the browser and exits shortly after the final adapter disconnects.

Plugin behavior

The plugin:

• registers the packaged browser MCP adapter;
• injects the active OpenCode session ID after model argument generation;
• exposes compact browser tools unless existing permissions require direct tools;
• releases owned tabs when an OpenCode session is deleted;
• registers the bundled browser automation skill.

OpenCode sees two compact tools by default:

• browser_dispatch executes one browser action.
• browser_help lists actions or loads one action schema.

If the plugin detects per-action browser_* permission or tool rules, it uses direct tools so those policies continue to work. Compact mode can also be disabled explicitly:

{
  "$schema": "https://opencode.ai/config.json",
  "plugin": [
    ["@mirsella/opencode-browser-mcp", { "compactTools": false }]
  ]
}

Architecture

flowchart LR
    O1[OpenCode instance A] --> A1[packaged stdio adapter]
    O2[OpenCode instance B] --> A2[packaged stdio adapter]
    A1 -->|private Unix socket| R[auto-managed broker]
    A2 -->|private Unix socket| R
    R --> T[CDP target tracker]
    R --> W[session worker pool]
    W --> C[chrome-devtools-mcp]
    T --> B[managed browser]
    C --> B
    B --> P[shared locked profile]

The adapter starts the broker on demand but does not own it. This lets adapters from separate OpenCode processes share one browser without tying its lifetime to whichever process connected first. Socket and profile locks make simultaneous startup race-safe and prevent two browsers from opening the same profile.

Each routed session leases its own chrome-devtools-mcp worker. Stable browser-level CDP target IDs remain the ownership authority; worker-local page numbers are removed from model-visible schemas and responses.

Ownership guarantees

• A tab has at most one owner.
• Routed sessions execute concurrently through separate workers.
• Popups inherit the owner of their opener tab.
• A session cannot select, inspect, or close another session's tabs through the broker.
• Manual and otherwise unowned tabs are not claimed during cleanup.
• Ownership conflicts, stale browser generations, and malformed responses fail closed.

These are routing guarantees, not an operating-system security boundary. Any process running as the same Unix user can connect directly to the browser's loopback CDP port.

Browser and profile

The plugin detects Chromium, Google Chrome, Helium, Brave, and Microsoft Edge. Chromium is preferred by default; OPENCODE_BROWSER_EXECUTABLE overrides automatic detection. Google Chrome 136 and newer ignore remote-debugging flags for its default data directory, so Chrome uses a dedicated directory under ~/.config/opencode-browser-mcp by default. Other detected browsers retain their existing profile defaults.

The broker starts Chromium lazily on the first browser action. For a headed browser it passes only a fixed allowlist of display and desktop variables. The current process environment stays authoritative; missing values are recovered from the current user session when available.

Optional environment variables inherited from OpenCode:

| Variable | Default | Purpose | | --- | --- | --- | | OPENCODE_BROWSER_EXECUTABLE | auto-detected | Chromium-family executable | | OPENCODE_BROWSER_PROFILE | browser-dependent | Shared browser data directory | | OPENCODE_BROWSER_HEADLESS | false | Run without a visible window | | OPENCODE_BROWSER_SESSION_LAYOUT | shared-window | shared-window or window-per-session | | OPENCODE_BROWSER_CDP_PORT | 9222 | Loopback CDP port | | OPENCODE_BROWSER_IDLE_MINUTES | 60 | Fallback cleanup for routed sessions | | OPENCODE_BROWSER_STARTUP_SECONDS | 20 | Browser startup deadline | | OPENCODE_BROWSER_OPERATION_SECONDS | 540 | Browser operation deadline | | OPENCODE_BROWSER_DOWNSTREAM_COMMAND | bunx | DevTools MCP launcher |

Lifecycle

| Event | Behavior | | --- | --- | | First adapter connects | One internal broker acquires the socket and profile leases | | Tools are listed | Chromium remains stopped | | First browser action | Chromium and the ownership tracker start | | OpenCode turn becomes idle | Owned tabs remain available for the next turn | | OpenCode session is deleted | Only that session's owned tabs close | | Routed session reaches the configured inactivity timeout | Fallback cleanup closes that session's owned tabs; defaults to 60 minutes and 0 disables it | | Another OpenCode instance connects | It shares the broker and profile with isolated tab ownership | | Final adapter disconnects | The broker waits briefly, closes Chromium, and exits | | Broker exits unexpectedly | A later adapter starts a replacement and recovery fails closed unless the exact browser generation matches |

Troubleshooting

• A headed startup error mentioning DISPLAY or WAYLAND_DISPLAY means no graphical session could be found. Set OPENCODE_BROWSER_HEADLESS=true when running without one.
• A profile or socket lease error means another live package process owns it or a stale process is still running. Do not bypass the locks.
• A process on the configured CDP port must belong to the exact managed browser generation. Stop it or choose another port.
• If downstream startup fails, verify that bunx is available to OpenCode.
• The plugin refuses to replace an unrelated mcp.browser entry.

Security

All sessions deliberately share cookies, authentication, storage, extensions, permissions, history, and downloads. Browser content remains untrusted and may contain prompt injection. The private same-UID socket prevents access by other local users, but it does not isolate processes already running as your Unix user.

Read SECURITY.md before using a profile with sensitive data.

Development

cargo fmt --check
cargo test --all-targets
cargo clippy --all-targets -- -D warnings
bun test tests/plugin.test.ts
cargo test --release --test e2e -- --ignored --nocapture

The headed E2E starts adapters against temporary profiles, sockets, and CDP ports. It checks automatic startup, startup races, cookie sharing, tab isolation, concurrent calls, active-call cleanup, reconnect grace, compact dispatch, both window layouts, and automatic browser shutdown.

| Path | Responsibility | | --- | --- | | plugin/ | OpenCode registration, session routing, and cleanup controls | | vendor/ | packaged native binary used directly by the OpenCode plugin | | src/broker.rs | adapter bridge, managed broker lifecycle, routing, and leases | | src/cdp.rs | stable CDP target tracking and ownership | | src/main.rs | browser supervision, workers, and response filtering | | src/persistence.rs | atomic generation-scoped ownership state | | tests/e2e.rs | startup, shared-profile, isolation, routing, and shutdown coverage |

See CONTRIBUTING.md for the development and release workflow.

License

MIT