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How to connect Customjs to Claude

Connect Claude Web, Desktop and Cowork to Customjs MCP. Convert this html invoice to pdf file, take a screenshot of your company homepage, and more using natural language, with authentication handled for you.

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Customjs is a code-first automation platform for integrating custom JavaScript logic across your tech stack. It lets you extend applications quickly by writing functions for tasks like emails, PDFs, or CRM updates.

5 Tools

Introduction

Claude is Anthropic's AI assistant, available on the web, in the desktop app, and on mobile. Cowork is its agent for knowledge work, and it runs on all of those surfaces too. Connected to your apps, Claude can work with your files and services to accomplish complex tasks on your behalf.

This guide walks you through the easiest and most secure way to connect your Customjs account to Claude via Composio Connect, enabling it to convert this HTML invoice to PDF file, take a screenshot of your company homepage, merge these three PDF reports into one, and more such actions on your behalf without compromising your account security.

Setup is the same on Claude Web, Desktop, and Cowork, and you only need to do it once. The connector is tied to your account, so it's available in all three.

Also integrate Customjs with

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Connecting Customjs to Claude Web, Desktop, and Cowork

Two ways to add the Composio connector. Pick whichever you prefer.

1. Add with one click

Click the button. Claude opens with the Composio connector filled in. Click Add, then go to step 2.

Add to Claude

Add manually

In Claude Desktop, click Customize in the left sidebar, then select Connectors and click the + icon at the top.

Claude Desktop connectors screen with Add custom connector selected

Click Add custom connector and paste in the Composio MCP server URL:

bash
https://connect.composio.dev/mcp
Add custom connector dialog with Composio MCP server URL

2. Authorize in your browser

Click Connect. You'll be redirected to a browser window where you can authorize Composio to continue.

Composio authorization screen for Claude Web, Desktop, and Cowork

3. Connect your Customjs account

Back in Claude, ask it to connect to Customjs or give it any Customjs-related task.

For example, ask Claude to:

  • "Convert this HTML invoice to PDF file"
  • "Take a screenshot of your company homepage"
  • "Merge these three PDF reports into one"

It will prompt you to authenticate and authorize access.

That's it. Composio's tools are now available in Claude, and your Customjs account is ready to use.

What is the Customjs Claude Connector, and what's possible with it?

The Customjs MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your Customjs account. It provides structured and secure access to your Customjs automations, so your agent can convert HTML to PDFs and images, capture website screenshots, merge PDF files, and run custom browser scripts on your behalf.

  • HTML to PDF and PNG conversion: Instantly generate high-quality PDFs or PNG images from any HTML markup or template using agent commands.
  • Automated webpage screenshot capture: Have your agent take precise, up-to-date screenshots of any public webpage for documentation, monitoring, or reporting.
  • PDF merging and file handling: Let your agent combine multiple PDF files into a single document, perfect for reports or document consolidation tasks.
  • Headless browser automation with Puppeteer: Empower your agent to execute custom Puppeteer scripts—scraping data or capturing advanced browser screenshots as PNGs.
  • Secure API key authentication: Ensure that all actions are performed securely by verifying your Customjs API key through the agent-managed authentication flow.

Troubleshooting

1. Why does Claude not use the Composio connector for Customjs?

The connector can show as connected, but Claude must use it in each Customjs conversation.

  • Click + at the lower left of the chat, or type /.
  • Hover Connectors.
  • Turn on Composio.
  • Ask Claude to connect to Customjs again.

2. Why does Claude show an MCP server error before Customjs connects?

Claude can show Couldn't reach the MCP server or Authorization with the MCP server failed when you add the connector for Customjs.

  • Check that the connector URL is https://connect.composio.dev/mcp.
  • Connectors run from Anthropic's cloud, so your device network is usually not the problem.
  • Add the connector again from Customize > Connectors, then ask Claude to connect Customjs.
  • If it fails again, send the error and the ofid_ reference id to support@composio.dev.

3. Why does the Customjs authorization link not work?

The Composio connector is one server. Your Customjs account connects separately when Claude asks for it.

  • If the browser does not open, or the link expires, ask Claude to retry the Customjs connection.
  • Composio creates a fresh Customjs authorization link.
  • Open that link in your browser and finish the Customjs sign-in.

4. Why do Customjs actions fail after they worked before?

The Customjs connection can expire or lose permission.

  • Ask Claude to inspect the Customjs connection.
  • If the connection is unhealthy, disconnect it when Claude prompts you.
  • Reconnect the Customjs account and retry the action.
  • If Claude shows a permission prompt, approve it before Claude changes data in Customjs.
  • If the action still fails with a permission error, check that the connected account has that permission in Customjs itself.

5. How do I switch to a different Customjs account?

Claude can manage the Customjs connection for you.

  • Ask Claude to disconnect or delete the current Customjs account.
  • Ask Claude to connect Customjs again.
  • Open the new Composio authorization link for Customjs.
  • Sign in with the other Customjs account in the browser.
  • After the account connects, ask Claude to retry the Customjs task.

6. Why is my Customjs connection missing in Claude Desktop or on a Team plan?

The connector belongs to your Claude account, so your Customjs connection works in Claude Web, Desktop, and Cowork.

  • In Claude Desktop, open Customize > Connectors.
  • Next to Composio, click ⋮ and click Clear cache.
  • If Customjs tools still do not appear, click ⋮, disconnect, remove the connector, and add it again.
  • On Team or Enterprise, an Owner or Primary Owner must enable the connector before you can connect Customjs.
TOOLS

Supported Tools

Every Customjs action and event your agent gets out of the box.

Authenticate CustomJS API Key

Authenticate and validate a CustomJS API key.

Convert HTML to PDF

Convert HTML content to a PDF document.

Convert HTML to PNG

Tool to convert HTML string to PNG image.

Merge multiple PDFs into one

Merge multiple PDF files from URLs into a single PDF document.

Run Puppeteer Script

Execute a Puppeteer script in a headless browser and capture a screenshot.

FRAMEWORKS

How to build Customjs MCP Agent with another framework

OpenAI Agents SDK logo

OpenAI Agents SDK

Use Customjs MCP with OpenAI Agents SDK

Claude Agent SDK logo

Claude Agent SDK

Use Customjs MCP with Claude Agent SDK

Claude Code logo

Claude Code

Use Customjs MCP with Claude Code

Codex logo

Codex

Use Customjs MCP with Codex

OpenClaw logo

OpenClaw

Use Customjs MCP with OpenClaw

Hermes logo

Hermes

Use Customjs MCP with Hermes

Atomic Agent logo

Atomic Agent

Use Customjs MCP with Atomic Agent

Google ADK logo

Google ADK

Use Customjs MCP with Google ADK

LangChain logo

LangChain

Use Customjs MCP with LangChain

Vercel AI SDK logo

Vercel AI SDK

Use Customjs MCP with Vercel AI SDK

Mastra AI logo

Mastra AI

Use Customjs MCP with Mastra AI

LlamaIndex logo

LlamaIndex

Use Customjs MCP with LlamaIndex

CrewAI logo

CrewAI

Use Customjs MCP with CrewAI

Pydantic AI logo

Pydantic AI

Use Customjs MCP with Pydantic AI

AutoGen logo

AutoGen

Use Customjs MCP with AutoGen

FAQ

Frequently asked questions

With a standalone Customjs MCP server, the agents and LLMs can only access a fixed set of Customjs tools tied to that server. However, with the Composio Tool Router, agents can dynamically load tools from Customjs and many other apps based on the task at hand, all through a single MCP endpoint.

Yes, you can. Claude Cowork fully supports MCP integration. You get structured tool calling, message history handling, and model orchestration while Tool Router takes care of discovering and serving the right Customjs tools.

Yes, absolutely. You can configure which Customjs scopes and actions are allowed when connecting your account to Composio. You can also bring your own OAuth credentials or API configuration so you keep full control over what the agent can do.

All sensitive data such as tokens, keys, and configuration is fully encrypted at rest and in transit. Composio is SOC 2 Type 2 compliant and follows strict security practices so your Customjs data and credentials are handled as safely as possible.

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