postback

A postback is a request initiated by the client to the server that submits data and triggers processing on the server side, typically resulting in a new or updated page. The term is commonly used in web applications and API integrations.

In traditional web applications, a postback occurs when a user submits a form; the browser sends an HTTP POST (or sometimes GET with data) to the same URL, and the server renders a fresh response, often preserving state via mechanisms like hidden fields or session data.

In frameworks such as ASP.NET, postback describes the page lifecycle step in which server controls raise events and the page reprocesses input before rendering again. Web pages may perform partial postbacks, where only portions of the page are updated via asynchronous techniques like AJAX, reducing full-page refresh.

In marketing and attribution, a postback URL is a server-to-server callback from a demand-side platform, affiliate network, or attribution service to notify a merchant of a conversion or event. Data typically includes identifiers to attribute the action to a prior click or impression; it is often delivered via HTTP POST.

In payments and e-commerce, postbacks refer to server-to-server notifications from gateways or processors to signal status changes such as authorization, capture, or settlement. They are used to reconcile orders independently of the user's browser and require secure handling and idempotent processing.

Security and reliability considerations include validating requests, authenticating sources, using encryption, ensuring idempotency to avoid double processing, and guarding against replay attacks. Postback mechanisms are widely used, but the user experience may differ if updates require a full page reload.