44API for AI agents
44API is a small validation service that checks VAT numbers, returns matching company details, and manages IP whitelists for API access. Finance and ops teams use it to verify billing data. 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 44API.
Validate a VAT number
Confirm a customer's VAT identifier is valid and pull back the registered company name before invoicing them.
List whitelisted IP addresses
Review which IP addresses currently have API access before deciding whether to add or remove one.
Add an IP to the whitelist
Grant a new server or office IP access to the account, a write action worth confirming before it takes effect.
4 44API actions, graded by risk.
Every 44API 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.
- 44api.list_whitelisted_ipsList Whitelisted IPs
- 44api.validate_vat_numberValidate VAT Number
write
1Create and change things. Allow, or ask the user first.
- 44api.add_whitelisted_ipAdd Whitelisted IP
destructive
1Delete, cancel or archive. Ask first, or deny outright.
- 44api.remove_whitelisted_ipRemove Whitelisted IP
44API in three steps.
- 01Your users connect 44APIThey add their 44API api key on Arc0 Connect, under your brand. It goes straight into the vault.
- 02You set the rulesReads run, writes like “add Whitelisted IP” can wait for the user, and “remove Whitelisted IP” can be denied outright.
- 03Any agent can actYour agent calls 44API through the Arc0 SDK or MCP, and so can Claude, ChatGPT and Cursor. Every call lands on the audit log.
await arc0.policies.set('44api', { read: 'allow', write: 'ask', // add_whitelisted_ip destructive: 'deny', // remove_whitelisted_ip }) # Claude Code: the same connection, one URL $ claude mcp add --transport http arc0 \ https://mcp.arc0.ai/u/u_8f2
How 44API connects.
Users add their 44API 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 44API 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 44API from any agent.
ClaudeChatGPTCursor
Codex
VS CodeOpenAI Agents SDKClaude Agent SDK
Vercel AI SDK
Mastra
LangGraphMore finance and accounting apps.
44API and Arc0, answered.
Can I use 44API with Claude, ChatGPT or Cursor?
Yes. Connect 44API 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 44API actions you allow.
How do users connect 44API?
Users add their 44API 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 44API actions can my agent take?
4 in total: 2 read, 1 write and 1 destructive, such as “add Whitelisted IP”. Your policies decide which of them each agent may call.
Can I stop my agent from deleting things in 44API?
Yes. Actions like “remove Whitelisted IP” 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 44API too?
Yes. The same 44API connection is available over REST and through the Arc0 proxy, so your product and your agent share one connection per user.
Plug 44API into your agent.
Your users connect 44API once, under your brand. Your agent gets 4 actions behind your policies, with every call on the record.
Free to build · MCP + REST · Audit log on every plan