---
title: "ETag and If-Match Headers"
description: "Ensuring Data Consistency with ETag and If-Match HTTP Headers"
lang: en
languages:
  en: https://docs.vismasoftware.no/vismanetapi/how-tos/etag/index.md
lastmod: 2026-02-18
---

> Documentation index: https://docs.vismasoftware.no/vismanetapi/how-tos/etag/llms.txt


# ETag and If-Match Headers

Last modified February 18, 2026

> Ensuring Data Consistency with ETag and If-Match HTTP Headers


## Overview

In modern web applications, ensuring data consistency and preventing conflicts is essential, especially when multiple clients attempt to update the same resource concurrently. The ETag and If-Match HTTP headers offer a solution for these challenges. Here's how they work together to maintain data integrity.

## ETag Response Header

An ETag (Entity Tag) is a unique identifier that the server assigns to a specific version of a resource. It is included in the response header when a client requests the resource. This identifier helps clients in managing cache and detecting resource changes.

- **Usage in API**: When a client requests a resource, the server responds with the ETag value in the response header and as part of the response DTO (with the field name: "**Timestamp**").
  
- **Pagination Note**: During paginated responses, the ETag value isn't included in the response header but is available within the response DTO (Field name: "**Timestamp**").

## If-Match Request Header (Optional)

The If-Match HTTP header is used by clients to signal that they wish to update a resource only if its current version matches a specific ETag. This mechanism prevents resource conflicts when multiple clients try to update the same resource simultaneously.

Refer to Also: [Lost Update Problem](https://www.w3.org/1999/04/Editing/#3.1), [If-Match](https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/If-Match), [HTTP conditional requests](https://developer.mozilla.org/en-US/docs/Web/HTTP/Guides/Conditional_requests).

- **Conflict Prevention**: If the ETag stored on the server doesn't match the client's If-Match header, the server responds with a 412 Precondition Failed status code.

- **Usage in API**: Currently, the "If-Match" header is optional and can only be used with certain PUT & POST action endpoints shared in detail in the following section below.

## Example

**1. GET**: .../v1/supplier/xxxxx

**Response headers**: ETag

![ETag](https://docs.vismasoftware.no/vismanetapi/how-tos/etag/etag.jpg)

**Response body**: timeStamp

![TimeStamp](https://docs.vismasoftware.no/vismanetapi/how-tos/etag/timestamp.jpg)

**2. PUT**: .../v1/supplier/xxxxx

**Request headers**: If-Match

![Header](https://docs.vismasoftware.no/vismanetapi/how-tos/etag/header.jpg)

This request will succeed in updating the resource only if the resource's current "ETag" is "AAAAAE0YIiI=".

**A. In case of success**, the server returns "204 - No content" together with the new ETag value in the response headers.
  
![ETag2](https://docs.vismasoftware.no/vismanetapi/how-tos/etag/etag2.jpg)

**B. In case of failure**, the server returns "412 - Precondition Failed".
  
![Message](https://docs.vismasoftware.no/vismanetapi/how-tos/etag/message2.jpg)

## Advantages of using ETag and If-Match

- **Optimistic concurrency control**: By using If-Match headers, clients can ensure that updates to resources are made safely without unwanted overwrites.

- **Data Integrity**: Helps maintain data consistency by validating that resource updates are based on the most current data.

## API Endpoints with ETag and If-Match Header Support

### Endpoints & Operations Supporting "ETag" Response Header

GET, PUT & POST operations on the following endpoints include an "etag" in the response header:

- Account
- Budget
- CashSale
- CashTransaction
- Contact
- Customer
- CustomerCreditWriteOff
- CustomerDebitNote
- CustomerInvoice
- CustomerOverdueCharge
- CustomerPayment
- Dimension
- Employee
- ExpenseClaim
- JournalTransaction
- PurchaseOrder
- PurchaseOrderBasic
- PurchaseReceipt
- PurchaseReceiptBasic
- Shipment
- Subaccount
- Supplier
- SupplierInvoice
- SupplierLocation
- SupplierPayment
- Timecard

Note: "TimeStamp" field can also be checked via the DTOs where it's exposed.

### Endpoints & Operations Supporting "If-Match" Request Header

- PUT Account
- PUT Budget
- PUT CashTransaction
- PUT CashSale
- PUT Contact
- PUT Customer
- PUT CustomerDebitNote
- PUT CustomerInvoice
- PUT CustomerOverdueCharge
- PUT CustomerPayment
- PUT Dimension
- PUT Employee
- PUT ExpenseClaim
- PUT JournalTransaction
- PUT PurchaseOrder
- PUT PurchaseOrderBasic
- PUT PurchaseReceipt
- PUT PurchaseReceiptBasic
- PUT Shipment
- PUT Subaccount
- PUT Supplier
- PUT SupplierInvoice
- PUT SupplierLocation
- PUT SupplierPayment
- PUT Timecard

**If the endpoint is asynchronous**, meaning that if it immediately returns a "202-Accepted" HTTP response and starts the actual job in the background, such as "Action"-based operations. (Endpoint URL: …/action/…)

If-Match is supported in the following actions only with "**erp-api-background** usage":

- POST CustomerDebitNote action/Release
- POST CustomerDebitNote action/sendToAutoInvoice
- POST CustomerOverdueCharge action/release
- POST CustomerPayment action/Release
- POST CustomerPayment action/Void
- POST SupplierPayment action/Release
- POST SupplierInvoice action/Release
- POST SupplierInvoice action/Prebook
- POST SupplierInvoice action/voidinvoice
- POST SupplierInvoice action/sendtoapproval

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[View this page](https://docs.vismasoftware.no/vismanetapi/how-tos/etag/)


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