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What is the ID5 Universal ID?

The ID5 Universal ID is a shared, neutral identifier that publishers and ad tech platforms can use to recognise users even in environments where 3rd party cookies are not available or blocked. ID5 enables publishers to create and distribute a shared 1st party identifier to the entire ecosystem. Ad tech platforms that connect with ID5 can decrypt the Universal ID and improve their user recognition capabilities. The ID5 Universal ID is designed to respect users' privacy choices throughout the advertising value chain.


The ID5 ID is free to use, but requires a simple registration with us. If you don’t already have an account with ID5, please visit to sign up and request your ID5 Partner Number to get started.

Stay up-to-date

We recommend that you sign up for our release notes in order to stay up-to-date with any changes to the implementation of the ID5 Universal ID in Prebid.

How does the ID5 Universal ID work?

By using the ID5 Universal ID, ad tech platforms can eliminate the need to sync their platform-specific IDs with their partners - the equivalent of needing a translator to help two people speaking different languages understand each other. When all platforms are using the Universal ID to transact against, it's like they're all speaking the same, common language. After configuring your Prebid.js setup to pull the ID5 Universal ID, your demand partners configured in Prebid can retrieve the ID and pass it on to their server side RTB partners (typically DSPs). This allows the DSP to target the user, manage frequency and recency capping, and apply additional data, even when cookies are not supported.

What will happen if I turn on the ID5 Universal ID on my page?

By activating the ID5 Universal ID, the following will take place:

  1. When a user is on your page, Prebid will make an asynchronous call to ID5 to retrieve the ID5 Universal ID.
  2. ID5 returns the ID5 Universal ID to Prebid, which will then store the result in a 1st party cookie with an expiration set by your config.
  3. On subsequent page loads, if the ID is already present in the cookie, there will be no need to call ID5 to retrieve the ID again, so there is minimal latency impact on your page
  4. Bid adapters that you have configured can choose to listen to the ID5 Universal ID within their adapter. If they do, they can pass the ID to their server.
  5. The bid adapter’s server can then include the ID5 Universal ID in any RTB bid requests as a separate field in the bid request
  6. The buyer can then use the ID5 Universal ID to lookup the user in their database and perform any targeting or capping that their campaigns require.

Setup Instructions

Below are step by step instructions for installing and configuring the Prebid.js User ID Module with the ID5 Universal ID. The instructions below assume a basic understanding of building Prebid.js and editing its page-level configuration; for more detailed instructions, getting started guides, and more, please visit the website.

Step 1: Build Prebid.js with the User ID Module

When building Prebid.js, be sure to include both the userId and id5IdSystem modules, in addition to the other modules you normally include.

gulp build –modules=userId,id5IdSystem

You may also use the Prebid Download page to build your version of Prebid.js by selecting the User ID: ID5 ID module.

Step 2: Configure the User ID Module in the page configuration

Within the pbjs.setConfig() function, add the following configuration before you make a request for bids:

  userSync: {
    userIds: [{
      name: "id5Id",
      params: {
        partner: 173,            // change to the Partner Number you received from ID5
        pd: "MT1iNTBjY..."       // optional, see below for a link to how to generate the `pd` string
      storage: {
        type: "html5",           // "html5" is the required storage type
        name: "id5id",           // "id5id" is the required storage name
        expires: 90,             // storage lasts for 90 days
        refreshInSeconds: 8*3600 // refresh ID every 8 hours to ensure it's fresh
    auctionDelay: 50             // 50ms maximum auction delay, applies to all userId modules


As of Prebid.js v4.13.0, ID5 requires storage.type to be "html5" and to be "id5id". Using other values will display a warning today, but in an upcoming release, it will prevent the ID5 module from loading. This change is to ensure the ID5 module in Prebid.js interoperates properly with the ID5 API and to reduce the size of publishers' first-party cookies that are sent to their web servers. If you have any questions, please reach out to us at

Generating the Publisher Data (pd) String

The pd string is available in version 3.25.0 of Prebid.js and later

The pd field (short for Publisher Data) is an optional, base64 encoded string that contains any deterministic user data the publisher has access to. The data will be used strictly to provide better linking of ID5 IDs across domains for improved user identification. If the user has not provided ID5 with a legal basis to process data, the information sent to ID5 will be ignored and neither used nor saved for future requests.

If the publisher does not have any Publisher Data to pass to ID5, the pd parameter can be omitted or left with an empty string value (pd: "").

The possible keys in the string are:

1sha256 hashed email
2sha256 hashed phone number
3cross-domain publisher user_id value
4cross-domain publisher user_id source (value provided by ID5)
5publisher user_id value


To illustrate how to generate the pd string, let's use an example. Suppose you have an email address for the user, in this example it is, and want to share it with ID5 to strengthen the value of the UID we respond with. You also have your own user id for this user that you can share: ABC123.

First, perform a sha256 hash of the email, resulting in a string b50ca08271795a8e7e4012813f23d505193d75c0f2e2bb99baa63aa822f66ed3

Next, create the raw pd string containing the keys 1 (for the hashed email) and 5 (for the publisher user id), separated by &’s (the order doesn't matter):


Finally, base64 the entire raw pd string, resulting in the final pd value:


This is the value you will add to the config when you initialize the ID5 userId module:

params: {
	partner: 173,   // change to the Partner Number you received from ID5

A Note About ID5 ID Encryption

The ID5 Universal ID that is delivered to Prebid will be encrypted by ID5 with a rotating key to avoid unauthorized usage and to enforce privacy requirements. Therefore, we strongly recommend setting storage.refreshInSeconds to 8 hours (8*3600 seconds) to ensure all demand partners receive an ID that has been encrypted with the latest key, has up-to-date privacy signals, and allows them to transact against it.

GDPR Support

The ID5 ID is a privacy-by-design implementation of a shared ID and fully supports the GDPR. When the ID5 ID is requested by Prebid in a GDPR-relevant country, ID5 will ensure the user has consented to processing by ID5 for the “Information storage and access” purpose (Purpose 1). If not, ID5 will not attempt to read or write our 3P cookie.

To enable GDPR support within Prebid, you will need to include the GDPR Consent Management module when you build Prebid:

gulp build –modules=userId,id5IdSystem,consentManagement

You will also need to ensure you add the appropriate configuration to your setConfig() function to include consentManagement:

    userSync: {
        userIds: [{
            name: "id5Id",
            params: {
                partner: 173,            // change to the Partner Number you received from ID5
				pd: "MT1iNTBjY..."       // optional, see above for how to generate the `pd` string
            storage: {
                type: "cookie",
                name: "id5id.1st",       // create a cookie with this name
                expires: 90,             // cookie lasts for 90 days
                refreshInSeconds: 8*3600 // refresh ID every 8 hours to ensure it is fresh
        auctionDelay: 50                 // allowing 50ms maximum auction delay
    consentManagement: {
        cmpApi: 'iab',
        timeout: 8000
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