What is Customaise MCP?
Customaise MCP connects an agent to the Customaise Chrome extension, a userscript manager built by CNDLE Studio LTD. The agent can read the current page's DOM and console, take screenshots of any tab, open and close tabs, and write two kinds of script: UserScripts, which change how a site looks and behaves for you, and AgentScripts, which register named tools on a page through the WebMCP standard so the agent can call them later. Everything runs in the Chrome you already use, with its logins.
The server is a Node.js package, @customaise/mcp, which also ships a customaise CLI for agents that have a shell instead of an MCP client. It exposes 21 tools and 5 resources, speaks stdio to the client and talks to the extension over a WebSocket on localhost port 4050. It needs Node.js 20, Chrome 147 or later and a signed-in Customaise account.
The repository, getcustomaise/customaise-mcp, is MIT-licensed with about 12 GitHub stars and mirrors the package from the company's private monorepo; v3.2.9 came out on 2 November 2026. The extension itself and the account backend are not open source.
How to install Customaise MCP
npx -y @customaise/mcpIs Customaise MCP worth it?
Customaise turns browser automation into a script library. Instead of clicking through a page each time, the agent inspects it once, writes an AgentScript that wraps the actions as named tools, installs it, and then calls those tools on later runs. That is cheaper and steadier than screenshot-driven control, and the same scripts are plain files the agent can edit and version.
The premise is also the risk. A script installed through the bridge runs in the page with your session cookies, so it can read and do anything you can on that site, from your inbox to your bank. The company has thought about this more than most. A script written through MCP or the CLI cannot grant its own tools allow; they fall back to prompt, which shows a consent modal and waits up to 5 minutes for you. The agent cannot answer that modal, set Always allow or turn on Full access. Marketplace subscriptions arrive disabled until you review the source.
The local bridge is narrower than many. The WebSocket on port 4050 accepts only the Customaise extension's origin, which stops an ordinary web page from connecting, but the README is frank that any native process running as you can forge that header. Two settings widen exposure: Full access lets eligible tools run without prompts across the browser profile, and Always allow is a permanent per-tool override. Page content the agent reads through get_page_context is untrusted input, so a prompt injection on a site could steer the agent into writing a harmful script, which the default prompt gate is there to catch.
The catch: this is a free tier on a commercial account, not a local tool. Every call needs a fresh sign-in token, the free cap is 50 calls a day, and WebMCP tool-call arguments travel to Customaise's backend, where the README says they are stored KMS-encrypted in Firestore with tool name, script name and origin kept in plain text. Claude Desktop and Cursor cap a tool call at 60 seconds, shorter than the consent wait, so an approved call can look failed. With about 12 stars, outside scrutiny has been thin.
Our take: Customaise suits someone who wants an agent to build lasting tools for the same few sites; for one-off automation, Playwright's throwaway browser keeps your real accounts out of the blast radius.
Where it earns its place
A front-end developer patching an internal admin console the team cannot change
Add a bulk-export button and hide noisy panels on a vendor dashboard
The agent reads the page with get_page_context, writes a UserScript, installs it with export_script, reloads and checks the console. A dozen iterations fit inside the free 50-call daily cap; heavier sessions need Power User at $9 a month.
An operations analyst at a 30-person logistics firm
Let an agent pull shipment status from a carrier portal that has no API
Have the agent wrap the portal's search and table reading in an AgentScript, with any write action declared prompt, then call it daily with call_webmcp_tool. Each call runs in the analyst's own session, so it inherits exactly their access.
A security lead deciding whether to allow the extension on work laptops
Judge what an agent could do through it
Check the agent-permission mode with get_bridge_status, keep Full access off, and require a separate Chrome profile with only low-risk logins. Remember that tool-call arguments reach Customaise's servers, which matters for regulated data.
Before you commit
- Setup
- Install the Customaise extension on Chrome 147 or later, sign in, turn on Agent Bridge, then add npx -y @customaise/mcp to Claude Code, Cursor, Codex, Kiro or Antigravity, or install the .mcpb bundle in Claude Desktop. Chrome's Allow user scripts toggle resets on every restart and has to be switched back on.
- Integrations
- 21 tools: script lifecycle (list, import, export, delete, toggle, sync), page and console context, tab control, screenshots, visually selected elements, WebMCP list and call, and Script Decisions settings; 5 resources with the scripting handbooks. Delete, export and call_webmcp_tool change state.
- Data and privacy
- Scripts and WebMCP tools act with your browser cookies on the sites they match. The bridge listens on ws://localhost:4050 in plain text, restricted by Origin header; the CLI daemon binds 127.0.0.1:4051 with a token file. WebMCP tool-call arguments go over HTTPS to Customaise's backend and are stored KMS-encrypted in Firestore, with metadata in plain text. Page content is untrusted input for prompt injection.
- Cost at scale
- Free accounts get 50 calls per UTC day and 150 per rolling 7 days, counting every successful tool dispatch; an agent building and testing a script uses several per iteration. Power User is $9 a month or $72 a year for unlimited calls.
- Limits
- Prompt-gated calls can block for up to 5 minutes, beyond the 60-second tool-call cap in Claude Desktop and Cursor. Chrome only. A failed sign-in check returns an error rather than running. Large DOM snapshots are written to files by default, so chat clients need CUSTOMAISE_MCP_OUTPUT=inline.
What’s good
- Agent-written scripts cannot grant themselves allow
- Turns repeated page work into reusable named tools
- WebSocket limited to the extension's origin
- Same tools from an MCP client or a shell CLI
What’s not
- Scripts run with your cookies on matched sites
- Requires a Customaise account; free cap of 50 calls a day
- Tool-call arguments stored on Customaise's backend
- Extension and backend are closed source
Best for
Developers who want an agent to build and maintain small tools for a handful of sites they use daily, and who will keep the default consent prompts on.
Customaise MCP alternatives
Customaise MCP: common questions
- Is Customaise MCP worth it?
- A careful bridge with a risky premise: your agent writes code that runs inside every logged-in site, so the consent settings deserve more attention than the tool list. We rate it 3.5 out of 5.
- How much does Customaise MCP cost?
- Free account with 50 agent tool calls per UTC day and 150 per rolling 7 days; Power User $9/month or $72/year for unlimited MCP and CLI calls.
- What are the downsides of Customaise MCP?
- Scripts run with your cookies on matched sites; requires a Customaise account; free cap of 50 calls a day; tool-call arguments stored on Customaise's backend; extension and backend are closed source.
- Who is Customaise MCP best for?
- Developers who want an agent to build and maintain small tools for a handful of sites they use daily, and who will keep the default consent prompts on.
- How much does Customaise MCP cost for a team or in production?
- Free accounts get 50 calls per UTC day and 150 per rolling 7 days, counting every successful tool dispatch; an agent building and testing a script uses several per iteration. Power User is $9 a month or $72 a year for unlimited calls.
- Is Customaise MCP safe for company data?
- Scripts and WebMCP tools act with your browser cookies on the sites they match. The bridge listens on ws://localhost:4050 in plain text, restricted by Origin header; the CLI daemon binds 127.0.0.1:4051 with a token file. WebMCP tool-call arguments go over HTTPS to Customaise's backend and are stored KMS-encrypted in Firestore, with metadata in plain text. Page content is untrusted input for prompt injection.
- What are the best Customaise MCP alternatives?
- The closest alternatives we have reviewed are OpenTabs, Playwright MCP and Chrome DevTools MCP.
Answers checked Nov 11, 2026.