REST API

A REST API is a web interface that follows the Representational State Transfer style, exposing resources at URLs that clients read and change with standard HTTP methods such as GET, POST, PUT and DELETE, usually exchanging JSON.

AI & Sales AutomationUpdated September 30, 2026

In short

A REST API lets programs work with another system's data over HTTP using URLs and standard methods.

Key points

  1. REST was defined by Roy Fielding in his 2000 doctoral dissertation as an architectural style for the web [1].
  2. Its constraints include a client-server split, stateless requests, cacheable responses and a uniform interface [1][2].
  3. HTTP semantics, including methods and status codes such as 200, 404 and 429, are defined in RFC 9110 [3].
  4. Access is usually authorized with an API Key or an OAuth token, and providers apply Rate Limiting per client [4].
  5. Most CRM (Customer Relationship Management) systems and outreach tools expose REST APIs, which is what makes Workflow Automation across tools possible.

The REST style

Roy Fielding described REST in 2000 as a set of constraints for building systems like the web [1]. In a REST API, everything is a resource with a URL, such as a contact, a deal or an email. Clients use HTTP methods to act on resources: GET reads, POST creates, PUT or PATCH updates and DELETE removes. Each request carries everything the server needs, so the server does not keep session state between calls, which makes REST APIs easier to scale [2]. Responses use standard HTTP status codes from RFC 9110 to report the outcome, for example 201 for created, 400 for a bad request and 404 for not found [3]. Most modern REST APIs send and receive JSON, and many are documented with an OpenAPI description.

Using REST APIs in sales tools

Sales stacks depend on REST APIs to share data. A CRM (Customer Relationship Management) API lets other tools create contacts, log activities and read deal stages. An outreach tool's API can accept new prospects, return reply status or pause a sequence. Enrichment services answer lookups through APIs, and a Waterfall Enrichment setup calls several of them in turn, and mailbox providers expose APIs for Email Sync. Calls are authorized with an API Key for server-to-server use or an OAuth token when acting for a user [4]. Providers enforce Rate Limiting, typically returning status 429 when a client sends too many requests, so integrations need to slow down and retry. Where near real-time updates matter, APIs are paired with webhooks, so the client does not have to poll for changes. Where a provider offers an API, it is usually a more stable and clearly permitted route to its data than Web Scraping the same pages.

The PineLead API

PineLead has an API, so teams can work with their PineLead data from their own code or connect it to other tools, such as a CRM (Customer Relationship Management) or internal reporting, instead of working only in the web app. PineLead finds new prospects every day, qualifies each one against the user's ICP criteria as a fit, a maybe or a reject, researches the company and writes a personalized draft. Those jobs are visible in the agent control panel. The same rules apply to the PineLead API as to any REST API: keep keys secret and out of source code, handle errors and limits gracefully, retry temporary failures with backoff, and log what your integration does so problems are easy to trace. Treat the prospect data you pull as Personal Data and store it with the same care as the rest of your stack.

Sources
  1. Architectural Styles and the Design of Network-based Software Architectures, Chapter 5 — Roy Fielding, UC Irvine
  2. What Is a REST API (RESTful API)? — IBM
  3. RFC 9110: HTTP Semantics — IETF
  4. REST — MDN Web Docs Glossary
External sources open in a new tab.

Related terms

API Key

An API key is a secret token that identifies your app to an API, so treat it like a password.

OAuth

OAuth lets you give an app scoped access to your account without handing over your password.

Rate Limiting

Rate limiting caps how fast a client can make requests, so one user or script cannot overwhelm a system.

Webhook

A webhook is an automatic HTTP callback that pushes an event to your system the moment it happens.

Workflow Automation

Workflow automation chains tasks together so that one event triggers the next steps on its own.

Mentioned in
AI Sales AgentCRM (Customer Relationship Management)Usage-Based PricingWeb Scraping

Outreach without the busywork.

PineLead finds new B2B prospects every day, qualifies them against your criteria and writes the first email in your voice. You approve — PineLead sends.

Start free with 100 credits →