What is the _rdt_em cookie?
_rdt_em is an HTTP cookie placed by Reddit when a webpage embeds the Reddit Ads pixel (Reddit Pixel) or Reddit widgets/buttons. It typically appears on sites running advertising campaigns on Reddit that want to measure conversions from those campaigns.
The cookie is set by the Reddit script loaded into the page, not directly by the host website, but it appears as a result of the site owner integrating Reddit's tracking code.
What data it stores
The cookie stores an identifier (token) that Reddit uses to link on-site events (page views, conversions) to a Reddit user or session, for advertising attribution purposes. The exact value format is not publicly documented by Reddit and may vary.
The collected data is sent to Reddit's servers (Reddit Inc., with possible processing in the US), where it is matched against the advertiser account's campaign activity.
What it is used for
For Reddit, _rdt_em helps measure ad campaign performance: how many people who saw or clicked a Reddit ad later completed an action (purchase, sign-up) on the advertiser's site.
For the website owner, this cookie provides conversion and retargeting data, useful for optimizing ad spend on the Reddit Ads platform.
Does it require consent?
_rdt_em is classified as a marketing/advertising cookie. Under GDPR (Regulation 2016/679) and the ePrivacy Directive (transposed in Romania via Law 506/2004), this type of cookie cannot be set before the visitor gives explicit consent.
Site owners must list _rdt_em in their cookie policy under the marketing category and ensure the Reddit script only loads after the user has consented.
How to block or delete _rdt_em
A visitor can manually delete or block this cookie from browser settings (Chrome, Firefox, Edge, Safari – cookie and site data management section), or use tracker-blocking browser extensions.
- Clearing cookies for reddit.com or the visited site removes _rdt_em
- Blocking third-party tracking scripts in the browser prevents it from being reset
For site owners, a CMP such as CookieFix can automatically block the Reddit pixel from loading until the visitor accepts the marketing category, ensuring _rdt_em is not set without consent.
Frequently asked questions
It is a marketing cookie set by Reddit through its Reddit Ads conversion pixel, used to measure ad performance and link site visits to a Reddit account or session.
It is a session cookie, so it is typically deleted automatically when the visitor closes the browser.
Yes, as a marketing/tracking cookie it requires the visitor's prior consent before being set, under GDPR and ePrivacy rules.
Use a CMP that blocks the Reddit Pixel script until the marketing category is accepted, or remove the Reddit Ads integration if it is not needed.