---
title: "SOAP"
description: "SOAP is an XML-based protocol for communication between applications. Learn how it works, the message structure and how it differs from REST."
url: "https://nodea.io/en/glossary/soap"
lang: "en"
updated: "2026-07-13"
---

# SOAP

> SOAP is an XML-based messaging protocol used to exchange data between applications in web services that require a strict contract and strong security.

**SOAP** (*Simple Object Access Protocol*) is an XML-based protocol for exchanging messages between applications running on different systems and in different programming languages. Unlike the [REST](https://nodea.io/en/glossary/rest) style, SOAP is a strictly defined protocol with a formal contract, which makes it popular in enterprise, banking and telecommunications environments.

## How SOAP works

Communication in SOAP is based on exchanging structured XML messages called envelopes. Every envelope has a fixed structure:

- **Envelope** — the root element wrapping the whole message,
- **Header** — optional metadata such as credentials or transaction details,
- **Body** — the actual request or response payload,
- **Fault** — a section describing any error.

A SOAP service is described by a WSDL file that precisely defines the available operations, data types and message structure — giving the client and server an unambiguous contract. SOAP is transport-independent: it most often runs over HTTP, but can also work through SMTP or other protocols. The WS-\* family of standards adds advanced features such as signatures, encryption and transactions.

## SOAP in practice

SOAP remains present wherever a formal contract, transactions and strong security matter — in banking, payment and insurance systems, and in integrations with public institutions. Many older but still-running enterprise [APIs](https://nodea.io/en/glossary/api) are built on SOAP. New, lightweight web integrations more often choose REST with the [JSON](https://nodea.io/en/glossary/json) format, yet knowing SOAP is essential when maintaining and connecting to existing enterprise-grade systems.

### How is SOAP different from REST?

SOAP is a rigid protocol based purely on XML, with a formal WSDL contract and built-in security standards. REST is a lighter architectural style that uses HTTP methods and, most often, JSON. SOAP is chosen where formalism and transactions matter; REST where simplicity and speed do.

## Related

- [REST](https://nodea.io/en/glossary/rest)
- [API](https://nodea.io/en/glossary/api)
- [Webhook](https://nodea.io/en/glossary/webhook)
- [JSON](https://nodea.io/en/glossary/json)
- [HTTP](https://nodea.io/en/glossary/http)

---

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