Customjs for AI agents
CustomJS runs custom JavaScript functions in the cloud, letting a team extend other systems with logic like generating PDFs or updating CRM fields. Connect it once through Arc0, and your agent, or Claude, ChatGPT and Cursor, can use it through one MCP endpoint, limited to what each user approved.
What agents do in Customjs.
Convert HTML to PDF
Convert an HTML page into a PDF document as part of an automated workflow.
Merge multiple PDFs
Merge several PDF files into one, useful for combining a set of reports.
Run a custom Puppeteer script
Run a custom Puppeteer script to automate a browser task not covered by a built-in action.
5 Customjs actions, graded by risk.
Every Customjs action is tagged read, write or destructive, so one policy covers the whole app and new actions inherit the right default.
read
2Look things up. Allowed by default.
- customjs.convert_html_to_pdfConvert HTML to PDF
- customjs.convert_html_to_pngConvert HTML to PNG
write
2Create and change things. Allow, or ask the user first.
- customjs.authenticate_api_keyAuthenticate CustomJS API Key
- customjs.run_puppeteer_scriptRun Puppeteer Script
destructive
1Delete, cancel or archive. Ask first, or deny outright.
- customjs.merge_pdfsMerge multiple PDFs into one
Customjs in three steps.
- 01Your users connect CustomjsThey add their Customjs api key on Arc0 Connect, under your brand. It goes straight into the vault.
- 02You set the rulesReads run, writes like “authenticate CustomJS API Key” can wait for the user, and “merge multiple PDFs into one” can be denied outright.
- 03Any agent can actYour agent calls Customjs through the Arc0 SDK or MCP, and so can Claude, ChatGPT and Cursor. Every call lands on the audit log.
await arc0.policies.set('customjs', { read: 'allow', write: 'ask', // authenticate_api_key destructive: 'deny', // merge_pdfs }) # Claude Code: the same connection, one URL $ claude mcp add --transport http arc0 \ https://mcp.arc0.ai/u/u_8f2
How Customjs connects.
Users add their Customjs api key on Arc0 Connect. It is encrypted in the vault, never shown to the model, and each user can rotate or revoke it at any time.
The same Customjs connection serves your agent over MCP and your own backend over REST and the proxy, so a user connects once. How Arc0 handles credentials →
- AUTH
- API key
- CREDENTIALS
- Per-tenant encrypted vault
- MODEL SEES
- Results only, never credentials
- AUDIT LOG
- Every call, on every plan
Use Customjs from any agent.
ClaudeChatGPTCursor
Codex
VS CodeOpenAI Agents SDKClaude Agent SDK
Vercel AI SDK
Mastra
LangGraph
Customjs and Arc0, answered.
Can I use Customjs with Claude, ChatGPT or Cursor?
Yes. Connect Customjs to Arc0 once, then add your Arc0 MCP URL to Claude, ChatGPT, Cursor, Claude Code or any other remote-MCP client. Each assistant only gets the Customjs actions you allow.
How do users connect Customjs?
Users add their Customjs api key on Arc0 Connect. It is encrypted in the vault, never shown to the model, and each user can rotate or revoke it at any time.
Which Customjs actions can my agent take?
5 in total: 2 read, 2 write and 1 destructive, such as “authenticate CustomJS API Key”. Your policies decide which of them each agent may call.
Can I stop my agent from deleting things in Customjs?
Yes. Actions like “merge multiple PDFs into one” are graded destructive. Set destructive actions to deny, or to ask so the user approves each one, and blocked calls still show up on the audit log.
Can my own backend call Customjs too?
Yes. The same Customjs connection is available over REST and through the Arc0 proxy, so your product and your agent share one connection per user.
Plug Customjs into your agent.
Your users connect Customjs once, under your brand. Your agent gets 5 actions behind your policies, with every call on the record.
Free to build · MCP + REST · Audit log on every plan