Developer Tools & Devops · Customjs + Claude
Customjs MCP with Claude: Run Custom JavaScript Automations Through Plain Language
The short answer
Claude connects to Customjs through the Model Context Protocol (MCP), a secure standard that lets Claude use software with permissions you control. Once connected with an API key, Claude can run your custom JavaScript functions, generate PDFs, send transactional emails and update CRM fields from plain-language instructions.
What is Customjs?
Customjs is a code-first automation platform for developers and technical teams. It lets you write custom JavaScript functions that connect your applications, handle tasks such as sending emails, creating PDF documents and updating records, and extend existing systems quickly. Engineering teams and operations leaders use it to link tools in their stack without building everything from scratch.
How Claude connects to Customjs through MCP
The Model Context Protocol is an open standard that works like a universal adapter between Claude and other software. It lets Claude securely use a tool, reading information and taking actions, with permissions that your organisation decides and controls. Customjs can be reached this way, so Claude can work with the functions and services you have already built.
Once connected, Claude can typically trigger your Customjs automations, request a generated PDF, send a transactional email, or update specific CRM fields when someone describes the task in everyday language. Staff do not need to remember function names or write requests in code.
Access is limited by the API key you issue. We set up least-privilege access so Claude only reaches the functions it needs, and we require people to approve consequential actions such as bulk updates or outgoing messages to customers. Every action is logged for review.
What you can automate
Automated customer onboarding documents
A sales operations manager asks Claude to generate a welcome pack PDF and send it by transactional email once a new account is confirmed. Claude runs the relevant Customjs functions with the account details, so the pack goes out within minutes instead of waiting for a manual export and attachment process.
CRM field updates from meeting notes
An account manager pastes call notes into a conversation with Claude. Claude identifies the renewal date, deal stage and next action, then updates the matching CRM fields through Customjs after the manager confirms the changes. Records stay current without manual data entry.
Invoice and statement generation
A finance team member requests monthly statements for a group of clients. Claude triggers the PDF generation function for each account, checks the results and sends the statements by email. Finance reviews exceptions before anything leaves the building.
Internal report distribution
A department head asks for the weekly operations summary to be produced and shared with the leadership team. Claude runs the report function, creates a formatted PDF and emails it to the agreed distribution list, keeping the process consistent every week.
Support escalation handling
A support lead asks Claude to flag accounts with overdue issues, update their CRM status and send a templated follow-up email. The team approves the list before messages go out, so customers receive timely and accurate communication.
An end-to-end workflow: New client welcome and CRM setup
TriggerA sales representative tells Claude that a contract has been signed for a new client.
Claude reads the client details the representative provides and checks them against the agreed format.
Claude runs a Customjs function to update the client's status, owner and contract dates in the CRM.
Claude triggers a Customjs PDF function to generate a personalised welcome pack.
The representative reviews the draft welcome email and the PDF in the approval step.
After approval, Claude sends the transactional email with the PDF attached and logs the completed actions.
OutcomeNew clients receive a consistent welcome pack on the same day the contract is signed, and CRM records are complete and accurate without manual re-keying across systems.
How we set it up
Free automation audit
We review your workflows, your current use of Customjs and the processes where Claude could save time. You leave with a clear list of the automations worth building first, at no cost.
Secure connection with an API key
We set up the Customjs connection using an API key, stored securely and scoped to the functions Claude needs. Access is least-privilege, so nothing beyond the agreed scope is exposed.
Workflow design and approvals
We design the end-to-end workflow across Customjs, your CRM, email and document systems. We define which actions run automatically and which need a person to approve them first.
Testing and launch with monitoring
We test the workflow against real past cases, then launch with monitoring and audit logs so every action can be reviewed. Any issues are fixed before wider use.
Team training and handover
We train your team on how to make requests, review approvals and read the logs. You receive documentation and ongoing support so the workflow stays reliable as your needs grow.
Who benefits
- Engineering and development teams
- Can expose existing Customjs functions to Claude without building a new interface, freeing time for core product work.
- Sales and account managers
- Keep CRM records up to date by describing changes in plain language, rather than navigating multiple screens.
- Operations and finance leaders
- Produce and distribute PDFs and reports on schedule, with approval steps that keep control with the team.
- IT and security heads
- Gain a governed connection with scoped API keys, approval gates and audit logs for every automated action.
Security and control
- Scoped API keys give Claude access only to the Customjs functions the workflow needs.
- People approve consequential actions such as customer emails, bulk record changes and financial documents.
- Audit logs record each request, action and approval so teams can review what happened.
- Test environments are used before launch, and changes are reviewed before they reach live data.
- API keys are rotated and revoked according to your security policy.
For teams in the US, UK, India and the Middle East
Organisations in the United States and the United Kingdom can choose hosting in their own region to align with local data protection expectations. Indian businesses can meet the Digital Personal Data Protection Act, 2023 by selecting India-based hosting and clear consent and retention rules. Organisations in the UAE and Saudi Arabia can align with local data protection laws by choosing a suitable hosting region. Hosting location is selected during design to meet your specific legal and contractual requirements.
Learn more about Claude and MCP
Anthropic's AI model and assistant.
Secure links between Claude and business tools.
How engineers build and change software with Claude.
Hosted agents that run multi-step work.
The open standard Claude uses to connect to tools.
Frequently asked questions
What does the Customjs MCP server do?
The Customjs MCP server acts as a secure bridge between Claude and your Customjs functions. It lets Claude see which automations are available and run them when asked. This means your existing JavaScript logic for emails, PDFs and CRM updates can be used through natural-language requests, without changing how the functions themselves work.
Is connecting Claude to Customjs secure?
Security depends on how the connection is set up. We use an API key scoped to the functions Claude needs, store it securely and rotate it on a schedule. Consequential actions require human approval, and every action is logged. We also test the setup before launch to confirm access is limited as intended.
What can Claude do with Customjs once connected?
Claude can typically run your custom JavaScript automations, generate dynamic PDFs, send transactional emails and update CRM fields. Requests are made in everyday language, and Claude chooses the right function. The exact actions available depend on the functions you have built and the permissions you grant.
How long does setup take?
Timelines depend on the number of workflows and the systems involved. A single, well-defined automation can often be connected and tested within a few weeks. Larger projects spanning several systems take longer. The free automation audit gives a realistic estimate once we understand your requirements.
Which plan or permissions do I need?
Generally, you need an active Customjs account with an API key that has permission to run the functions you want Claude to use. Your administrator controls these permissions. We confirm the exact requirements during the free audit, so you know what to prepare before setup begins.