What Is Custom API Integration?

A custom API integration is code you write to connect two systems through their APIs, when no prebuilt connector does the job the way you need it done.

The code calls one system's API, reshapes the response and sends it to the other system's API. Your team owns that code, so your team owns the error handling, the retries and the upkeep.

Why it matters for outbound

Prebuilt connectors cover the common path: push a lead to a CRM, add a contact to a sequence. They break down on your own rules. Skip accounts that already have an open deal. Route by territory. Write the email status into a custom field and block sends to anything risky.

A custom integration lets you encode those rules once and run them on every record. The cost is maintenance. APIs change, rate limits bite and someone has to watch the logs. Build custom when the rule is specific to your process. Use a connector when the default behavior is what you want. For a comparison of prebuilt options, see B2B prospecting software with the best integrations.

Example

A team wants every new inbound signup at acme.com enriched and routed to the right rep. No connector does their routing rule, so they write a small job.

curl -X POST https://api.leadocean.io/v1/people/enrich \
  -H "x-api-key: $LEADOCEAN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"email": "jane.doe@acme.com"}'

The job then runs three steps:

1. Receive the signup from the form's webhook.
2. Call the enrich endpoint above and read title, seniority and company.
3. Write those fields to the CRM through its own API and assign an owner.

Step 3 is where the custom part lives. It is also the part that fails when the CRM changes a field name, so log every response.

In LeadOcean data

LeadOcean is the data source in an integration like this. It is a REST API at https://api.leadocean.io, authenticated with the x-api-key header, with a 100 requests per second limit per key on every plan. The endpoints you would wire in are POST /v1/people/enrich, POST /v1/companies/enrich, /v1/people/search, /v1/companies/search and POST /v1/exports (openapi.json, September 2026).

For agent-based work there is a hosted MCP server at https://api.leadocean.io/mcp with 12 tools. It signs in with OAuth 2.1, so no key is pasted into a config. LeadOcean is not a CRM or a sequencer, and the app has no workflow builder. The app at app.leadocean.io has an Exports page for CSV downloads, which covers one-off pulls without code.

Check /pricing for the plans. The Free plan has 1,000 records, one-off, with no card, and it uses the same API as Pro.

Related terms

• API
• RESTful API
• Enrichment