Usable Browser Agent

Usable Browser Agent (free personal / evaluation tier)

An MCP server plus a browser extension that lets your AI agent (Claude Code, Codex, or any MCP client) drive your real browser, with all your logged-in sessions, instead of a throwaway automated browser. You log in once, by hand, and the agent operates as you.

This repository is the free tier: the same single-session MCP server as the commercial build, licensed for personal, non-commercial use and for evaluating the product before buying. The Firefox extension for it is published on Firefox Add-ons. Commercial use (in or for a business, in paid client work, or inside a commercial product or service) needs the commercial license, a one-time $39 purchase at https://savvytechsphere.com/usable-browser-agent, which also includes the Chrome build. It comes with a 14-day, no-questions refund. There is no license key in either tier and nothing checks for one; the tiers differ only in the license grant and the extension identity.

Your passwords stay out of the agent. When the agent logs you in, it passes only a secret

*alias*, never the value. Credentials live in a local vault, are domain-locked (refused on the

wrong site), and are redacted from everything the agent reads or screenshots. See

docs/CREDENTIAL-SAFETY.md.

How it works

Claude Code / Codex / any MCP client

| MCP over stdio v MCP server (Node, this repo) --hosts--> WebSocket ws://127.0.0.1:8876 ^ ^ | 53 browser_* tools | (extension connects out) +------------------------------------------+ Firefox extension (from Firefox Add-ons) your real profile, your logins -> DOM actions on the active tab

The agent perceives pages through an accessibility/DOM snapshot where every interactive element has a stable [ref=eN] handle, then clicks and types by ref. No coordinate guessing, no vision model required. Everything runs on your machine: MCP over stdio, and the extension talks to the server over a WebSocket bound to 127.0.0.1. Nothing leaves your computer.

The agent always acts on the currently active tab. Keep the tab you want it to use focused.

Get started (about 2 minutes)

Two pieces: this MCP server, which your agent launches, and the Firefox extension, which you install once from Firefox Add-ons.

1. Get the server and run the installer

Needs Node.js 18 or newer and Firefox 142 or newer (macOS first; see docs/INSTALL.md).

npm install -g usable-browser-agent

uba-install

Or from a checkout of this repository:

git clone https://github.com/Savvy-Tech-Sphere/usable-browser-agent-free.git

cd usable-browser-agent-free node bin/uba-install.mjs # or: npm run setup

(Prefer a download? Grab the zip from the Releases page, unpack it, and run the same command inside the folder.)

The installer checks Node and the port, installs dependencies, registers the MCP server with Claude Code and/or Codex using this copy's absolute path, runs the smoke test, optionally stores your first login, and prints the macOS permission steps. It is idempotent; re-running it never clobbers an existing config. Pass --non-interactive to accept every default.

2. Install the Firefox extension (one time)

Install Usable Browser Agent (free) from Firefox Add-ons: https://addons.mozilla.org/firefox/addon/usable-browser-agent-free/

The toolbar badge shows off, then ON once the extension connects to the MCP server your agent launched. (The installer also prints these steps, plus the .xpi and Chrome steps that apply to the commercial bundle; for the free tier the Add-ons listing is all you need.)

3. Log in and go

Log into the site(s) you want the agent to use, then ask your agent to run a browser task, for example: *"On the active tab, open my notifications and list the pull requests waiting on me."* It will snapshot the page, then act by ref.

Wiring by hand instead of the installer:

# Claude Code (user scope, works from anywhere afterward):

claude mcp add browser --scope user -e UBA_PORT=8876 -- node "$PWD/server/index.js"

# Codex: add to ~/.codex/config.toml (use the absolute path to your copy):

[mcp_servers.browser] command = "node" args = ["/ABSOLUTE/PATH/TO/usable-browser-agent-free/server/index.js"]

[mcp_servers.browser.env] UBA_PORT = "8876"

Help: docs/INSTALL.md, docs/TROUBLESHOOTING.md, docs/UNINSTALL.md.

Hardened mode is the default

browser_eval (arbitrary JavaScript in the page) is off unless you opt in, and screenshots are blocked near password fields. CAPTCHAs, anti-bot walls and two-factor prompts are deliberately not automated: the agent asks you to step in, since it is your browser on your screen. One active tab at a time.

Usage

1. Open Firefox or Chrome, log into the site(s) you want the agent to use.
2. Make sure the extension badge shows ON.
3. Ask Claude Code / Codex to do something — e.g. *"On the active tab, search for X and add the first result to the cart."* It will snapshot the page, then act by ref.

Workflow memory

Usable Browser Agent keeps a local workflow memory so agents do not rediscover the same changing website flow every time. This is for reusable task knowledge such as "how to create a new app in Google Play Console", including current page names, visible button labels, gotchas, and successful step order.

Default file:

~/.local/state/usable-browser-agent/workflow-memory.jsonl

Override with UBA_MEMORY_FILE=/path/to/workflow-memory.jsonl. The file is append-only JSONL, created with mode 0600. Normal recall ignores records that have been superseded or forgotten. This memory is local to the machine and file path you configure; it is not synced unless you point multiple agents at the same controlled file.

Expected agent loop:

1. Before a repeated or multi-step site task, call browser_workflow_recall with the task and/or site.
2. Use any matching memory as a starting point, then verify against the live page with browser_snapshot.
3. After a new or changed path succeeds, call browser_workflow_remember with the durable steps.
4. If an old memory is wrong, save a replacement with supersedes: ["old_id"], or call browser_workflow_forget if it should disappear from recall.

browser_status, browser_info, browser_navigate, and browser_snapshot also return short workflow-memory hints when the active tab's domain already has saved memories. Hints are intentionally brief; call browser_workflow_recall for the full steps.

Do not save passwords, one-time codes, raw account identifiers that are not needed for the workflow, or transient [ref=eN] handles. The memory store rejects saved steps containing transient refs and sanitizes stored URLs by dropping query strings and replacing likely account/app/developer id path segments. Save visible labels and page/section names instead, because refs are rebuilt after every snapshot.

Credential broker

browser_login and browser_fill_secret let an agent trigger a login without ever receiving the credential value. The MCP client passes only a secret alias and element refs. Plaintext flows only:

secrets file -> MCP server -> local WebSocket -> browser extension -> DOM field

The default vault file is ~/.config/usable-browser-agent/secrets.json; override it with UBA_SECRETS_FILE=/path/to/secrets.json. The server creates the parent directory if needed and warns if the secrets file is readable by group/other users; keep it at mode 0600.

The file is a JSON array:

[

{ "alias": "github", "domains": ["github.com"], "username": "octo@example.com", "password": "replace-with-real-secret" } ]

domains are allowed hostnames. Exact and subdomain matches are allowed, so github.com matches gist.github.com but not evilgithub.com.

For logins, prefer the atomic fill-and-submit tool after taking a snapshot:

browser_login({

"secret": "github", "username_ref": "e12", "password_ref": "e13", "submit_ref": "e14" })

browser_login fills the username when username_ref is provided and the secret has a username, fills the password, then submits in one extension action. If submit_ref is omitted, it submits the password field's enclosing form, with Enter as a fallback. The tool returns only a status string such as logged in via [e14] or submitted form.

browser_fill_secret remains available for non-login flows:

browser_fill_secret({ "ref": "e12", "secret": "github", "field": "username" })

browser_fill_secret({ "ref": "e13", "secret": "github", "field": "password" })

There is intentionally no value argument. If the active tab host is not allowed for the alias, the server refuses the fill and does not send the value to the browser.

Read-back and screenshots are protected in layers:

• Password fields and fields filled by the credential broker are redacted in snapshots and browser_get_value.
• browser_screenshot is blocked while a broker fill/login is in progress, while a populated password field is present, or while any field is marked as secret-filled. After login navigation removes the credential fields, screenshots are allowed again.
• The server lazily loads the vault for redaction and scrubs configured secret values from every outbound tool result, including browser_read_text and browser_eval results.

Hardened mode is on by default: browser_eval (the arbitrary-JS escape hatch) is disabled and screenshots are blocked whenever any password field exists, even if empty. If you need the browser_eval escape hatch, opt out by setting UBA_STRICT_SECRETS=0 in the server's environment. For Claude Code, browser is already registered, and claude mcp add refuses an existing name, so remove and re-add it, keeping UBA_PORT at the port you installed with (run from your install folder):

claude mcp remove browser --scope user && \

claude mcp add browser --scope user -e UBA_PORT=8876 -e UBA_STRICT_SECRETS=0 -- node "$PWD/server/index.js"

If you installed with UBA_SECRETS_FILE set, add -e UBA_SECRETS_FILE= to that command as well, or the server falls back to the default vault and your stored logins stop resolving. Re-running the installer prints the exact command for your copy.

For Codex, add UBA_STRICT_SECRETS = "0" under [mcp_servers.browser.env]. Restart the agent so the server picks it up.

Screenshot blocking is a temporal/state guard. Region-masking credential fields within an otherwise returned image is a possible v2 and is not implemented yet.

Tools (53)

| browser_login | Atomic