Spec: Common Fields

In the Segment Spec all the API calls have a common structure, and a few common fields.

However, not all destinations accept all fields included in the Spec. Not sure which fields a destination accepts? Refer to the destination’s documentation page, or check out the open-source destination code on GitHub.


Every API call has the same core structure and fields. These fields describe user identity, timestamping, and mechanical aides like API version.

Here’s an example of these common fields in raw JSON:

  "anonymousId": "507f191e810c19729de860ea",
  "context": {
    "active": true,
    "app": {
      "name": "InitechGlobal",
      "version": "545",
      "build": "",
      "namespace": "com.production.segment"
    "campaign": {
      "name": "TPS Innovation Newsletter",
      "source": "Newsletter",
      "medium": "email",
      "term": "tps reports",
      "content": "image link"
    "device": {
      "id": "B5372DB0-C21E-11E4-8DFC-AA07A5B093DB",
      "advertisingId": "7A3CBEA0-BDF5-11E4-8DFC-AA07A5B093DB",
      "adTrackingEnabled": true,
      "manufacturer": "Apple",
      "model": "iPhone7,2",
      "name": "maguro",
      "type": "ios",
      "token": "ff15bc0c20c4aa6cd50854ff165fd265c838e5405bfeb9571066395b8c9da449"
    "ip": "",
    "library": {
      "name": "analytics.js",
      "version": "2.11.1"
    "locale": "en-US",
    "network": {
      "bluetooth": false,
      "carrier": "T-Mobile US",
      "cellular": true,
      "wifi": false
    "os": {
      "name": "iPhone OS",
      "version": "8.1.3"
    "page": {
      "path": "/academy/",
      "referrer": "",
      "search": "",
      "title": "Analytics Academy",
      "url": "https://segment.com/academy/"
    "referrer": {
      "id": "ABCD582CDEFFFF01919",
      "type": "dataxu"
    "screen": {
      "width": 320,
      "height": 568,
      "density": 2
    "groupId": "12345",
    "timezone": "Europe/Amsterdam",
    "userAgent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/ Safari/537.36",
    "userAgentData": {
      "brands": [
          "brand": "Google Chrome",
          "version": "113"
          "brand": "Chromium",
          "version": "113"
          "brand": "Not-A.Brand",
          "version": "24"
      "mobile": false,
      "platform": "macOS"
  "integrations": {
    "All": true,
    "Mixpanel": false,
    "Salesforce": false
  "event": "Report Submitted",
  "messageId": "022bb90c-bbac-11e4-8dfc-aa07a5b093db",
  "receivedAt": "2015-12-10T04:08:31.909Z",
  "sentAt": "2015-12-10T04:08:31.581Z",
  "timestamp": "2015-12-10T04:08:31.905Z",
  "type": "track",
  "userId": "97980cfea0067",
  "version": 2

In more detail these common fields for every API call are:

Field Type Description
anonymousId required; optional if userID is set instead String A pseudo-unique substitute for a User ID, for cases when you don’t have an absolutely unique identifier. A userId or an anonymousId is required. See the Identities docs for more details.
context optional Object Dictionary of extra information that provides useful context about a message, but is not directly related to the API call like ip address or locale See the Context field docs for more details.
integrations optional Object Dictionary of destinations to either enable or disable See the Destinations field docs for more details.
messageId implicit String Automatically collected by Segment, a unique identifier for each message that lets you find an individual message across the API.
receivedAt implicit Date Automatically set by Segment, the timestamp of when a message is received by Segment It is an ISO-8601 date string. See the Timestamps fields docs for more detail.
sentAt optional Date Timestamp of when a message is sent to Segment, used for clock skew correction It is set automatically by the Segment tracking libraries. It is an ISO-8601 date string. See the Timestamps fields docs for more detail.
timestamp optional Date Timestamp when the message itself took place, defaulted to the current time by the Segment Tracking API, as a ISO-8601 format date string. If the event just happened, leave it out and we’ll use the server’s time. If you’re importing data from the past, make sure you to provide a timestamp.See the Timestamps fields docs for more detail.
type implicit String Type of message, corresponding to the API method: 'identify', 'group', 'track', 'page', 'screen' or 'alias'.
userId required; optional if anonymousID is set instead String Unique identifier for the user in your database. A userId or an anonymousId is required. See the Identities docs for more details.
version implicit Number Version of the Tracking API that received the message, automatically set by Segment.

Beyond this common structure, each API call adds a few specialized top-level fields.


Context is a dictionary of extra information that provides useful context about a datapoint, for example the user’s ip address or locale. You should only use Context fields for their intended meaning.

Field Type Description
active Boolean Whether a user is active.

This is usually used to flag an .identify() call to just update the traits but not “last seen.”
app Object dictionary of information about the current application, containing name, version, and build.

This is collected automatically from the mobile libraries when possible.
campaign Object Dictionary of information about the campaign that resulted in the API call, containing name, source, medium, term, content, and any other custom UTM parameter.

This maps directly to the common UTM campaign parameters.
device Object Dictionary of information about the device, containing id, advertisingId, manufacturer, model, name, type, and version.
ip String Current user’s IP address.
library Object Dictionary of information about the library making the requests to the API, containing name and version.
locale String Locale string for the current user, for example en-US.
network Object Dictionary of information about the current network connection, containing bluetooth, carrier, cellular, and wifi. If the context.network.cellular and context.network.wifi fields are empty, then the user is offline.
os Object Dictionary of information about the operating system, containing name and version.
page Object Dictionary of information about the current page in the browser, containing path, referrer, search, title and url. This is automatically collected by Analytics.js.
referrer Object Dictionary of information about the way the user was referred to the website or app, containing type, name, url, and link.
screen Object Dictionary of information about the device’s screen, containing density, height, and width.
timezone String Timezones are sent as tzdata strings to add user timezone information which might be stripped from the timestamp, for example America/New_York.
groupId String Group / Account ID.

This is useful in B2B use cases where you need to attribute your non-group calls to a company or account. It is relied on by several Customer Success and CRM tools.
traits Object Dictionary of traits of the current user.

This is useful in cases where you need to track an event, but also associate information from a previous Identify call. You should fill this object the same way you would fill traits in an identify call.
userAgent String User agent of the device making the request.
userAgentData Object The user agent data of the device making the request. This always contains brands, mobile, platform, and may contain bitness, model, platformVersion,uaFullVersion, fullVersionList, wow64, if requested and available.

This populates if the Client Hints API is available on the browser.

This may contain more information than is available in the userAgent in some cases.
channel String where the request originated from: server, browser or mobile

Context fields automatically collected

Below is a chart that shows you which context variables are populated automatically by the iOS, Android, and analytics.js libraries.

Other libraries only collect context.library, any other context variables must be sent manually.

Context Field Analytics.js Analytics-ios Analytics-android
  • IP Address isn’t collected by Segment’s libraries, but is instead filled in by Segment’s servers when it receives a message for client side events only.

IPv6 Addresses are not Supported

Segment does not support collection of IP addresses that are in the IPv6 format.

  • The Android library collects screen.density with this method.

  • userAgentData is only collected if the Client Hints API is available on the browser.

  • Segment doesn’t collect or append to the context of subsequent calls in the new mobile libraries (Swift, Kotlin, and React Native).

To pass the context variables which are not automatically collected by Segment’s libraries, you must manually include them in the event payload. The following code shows how to pass groupId as the context field of Analytics.js’s .track() event:

analytics.track("Report Submitted", {},
    {"groupId": "1234"}

To add fields to the context object in the new mobile libraries, you must utilize a custom plugin. Documentation for creating plugins for each library can be found here:


A dictionary of destination names that the message should be sent to. 'All' is a special key that applies when no key for a specific destination is found.

Integrations defaults to the following:

  All: true,
  Salesforce: false,

This is because Salesforce has strict limits on API calls.

Sending data to the rest of Segment’s destinations is opt-out so if you don’t specify the destination as false in this object, it will be sent to rest of the destinations that can accept it.


Every API call has four timestamps, originalTimestamp, timestamp, sentAt, and receivedAt. They’re used for very different purposes.

All timestamps are ISO-8601 date strings, and are in the UTC timezone. To see the user’s timezone information, check the timezone field that’s automatically collected by client-side libraries.

You must use ISO-8601 date strings that include timezones when you use timestamps with Engage. If you send custom traits without a timezone, Segment doesn’t save the timestamp value.

Timestamp overview

Timestamp Calculated Description
originalTimestamp Time on the client device when call was invoked
The timestamp value manually passed in through server-side libraries.
Used by Segment to calculate timestamp.

Note: originalTimestamp is not useful for analysis since it’s not always trustworthy as it can be easily adjusted and affected by clock skew.
sentAt Time on client device when call was sent.
sentAt value manually passed in.
Used by Segment to calculate timestamp.

Note: sentAt is not useful for analysis since it’s not always trustworthy as it can be easily adjusted and affected by clock skew.
receivedAt Time on Segment server clock when call was received Used by Segment to calculate timestamp, and used as sort key in Warehouses.

Note: For max query speed, receivedAt is the recommended timestamp for analysis when chronology does not matter as chronology is not ensured.
timestamp Calculated by Segment to correct client-device clock skew using the following formula:
receivedAt - (sentAt - originalTimestamp)
Used by Segment to send to downstream destinations, and used for historical replays.

Note: Recommended timestamp for analysis when chronology does matter.


The originalTimestamp tells you when call was invoked on the client device or the value of timestamp that you manually passed in.

Note: The originalTimestamp timestamp is not useful for any analysis since it’s not always trustworthy as it can be easily adjusted and affected by clock skew.


The sentAt timestamp specifies the clock time for the client’s device when the network request was made to the Segment API. For libraries and systems that send batched requests, there can be a long gap between a datapoint’s timestamp and sentAt. Combined with receivedAt, Segment uses sentAt to correct the original timestamp in situations where a user’s device clock cannot be trusted (mobile phones and browsers). The sentAt and receivedAt timestamps are assumed to occur at the same time (maximum a few hundred milliseconds), and therefore the difference is the user’s device clock skew, which can be applied back to correct the timestamp.

Note: The sentAt timestamp is not useful for any analysis since it’s tainted by user’s clock skew.

Segment now adds `sentAt` to a payload when the batch is complete and initially tried to the Segment API for the Swift, Kotlin, and C# mobile libraries

This update changes the value of the Segment-calculated timestamp to align closer with the receivedAt value rather than the originalTimestamp value. For most users who are online when events are sent, this does not significantly impact their data. However, if your application utilizes an offline mode where events are queued up for any period of time, the timestamp value for those users now more closely reflects when Segment received the events rather than the time they occurred on the users’ devices.


The receivedAt timestamp is added to incoming messages as soon as they hit the API. It’s used in combination with sentAt to correct clock skew, and also to aid with debugging libraries and systems that deliver events in batches.

The receivedAt timestamp is most important as the sort key in Segment’s Warehouses product. Use this for max query speed when retrieving data from your Warehouse.

Note: Chronological order of events is not ensured with receivedAt.


The timestamp timestamp specifies when the data point occurred, corrected for client-device clock skew. This is the timestamp that is passed to downstream destinations and used for historical replays. It is important to use this timestamp for importing historical data to the API.

If you are using the Segment server Source libraries, or passing calls directly to the HTTP API endpoint, you can manually set the timestamp field. This change updates the originalTimestamp field of the Segment event. If you use a Segment Source in device mode, the library generates timestamp and you cannot manually set one directly in the call payload.

Segment calculates timestamp as timestamp = receivedAt - (sentAt - originalTimeStamp).

For client-side tracking it’s possible for the client to spoof the originalTimeStamp, which may result in a calculated timestamp value set in the future.

This page was last modified: 24 Jun 2024

Get started with Segment

Segment is the easiest way to integrate your websites & mobile apps data to over 300 analytics and growth tools.
Create free account