> ## Documentation Index > Fetch the complete documentation index at: https://docs.formo.so/llms.txt > Use this file to discover all available pages before exploring further. # Common fields > Reference for the common and contextual fields shared across all Formo events, including event type, timestamps, device context, and session identifiers. Formo defines some common fields (event type, timestamps, and more) across all API calls that make up the core event data structure. This guide covers the common and contextual fields in detail. ## Common Fields > The Formo SDKs populate the required information automatically. | Name | Datatype | Required | Description | | :------------------- | :-------- | :------- | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `type` | String | ✓ | Captures the type of event. Values can be either identify, track, connect, signature, transaction, and others. | | `channel` | String | ✓ | Identifies the source of the event. The Formo SDKs emit `web`, `mobile`, `server`, or `source`. Other values such as `onchain`, `import`, and `api` are reserved for platform and import-pipeline ingestion, not SDK-emitted events. | | `version` | String | ✓ | Version of the event spec. | | `project_id` | String | ✓ | Unique identification for the project in the database. | | `session_id` | String | ✓ | Privacy-friendly daily changing session identifier. | | `anonymous_id` | String | ✓ | Pseudo-identifier for the user in cases where userId is absent. Equivalent to a device ID. | | `user_id` | String | | Unique identification for the user in the database. | | `address` | String | | Unique wallet address of the user. | | `event` | String | | Captures the user action that you want to record. | | `context` | Object | ✓ | Contains all additional user information. | | `properties` | Object | | Passes all relevant information associated with the event. | | `original_timestamp` | Timestamp | ✓ | Records the actual time (in UTC) when the event occurred. | | `sent_at` | Timestamp | ✓ | Captures the time (in UTC) when the event was sent from the client to Formo. | | `received_at` | Timestamp | ✓ | Time in UTC when Formo ingests the event. | | `timestamp` | Timestamp | ✓ | Formo calculates this field to account for any client-side clock skew using the formula: timestamp = received\_at - (sent\_at - original\_timestamp). Note that this time is in UTC. | | `message_id` | String | ✓ | Unique identification for the event. | ## Contextual Fields Contextual fields give additional information about a particular event. The following table describes the available contextual fields. | Name | Datatype | Required | Description | | :---------------- | :------- | :------- | :---------------------------------------------------------------------- | | `user_agent` | String | | The user agent of the device that you are tracking. | | `locale` | String | | Captures the language of the device. | | `location` | String | | Geographic location of the user. | | `timezone` | String | | Captures the timezone of the user you are tracking. | | `referrer` | String | | The referrer URL where the user came from. | | `utm_source` | String | | Identifies which site sent the traffic. | | `utm_medium` | String | | Identifies what type of link was used. | | `utm_campaign` | String | | Identifies a specific product promotion or strategic campaign. | | `utm_term` | String | | Identifies search terms. | | `utm_content` | String | | Identifies what specifically was clicked to bring the user to the site. | | `ref` | String | | Referral code or identifier. | | `gclid` | String | | Google Ads click identifier. | | `gad_source` | String | | Google Ads source parameter (newer attribution). | | `fbclid` | String | | Meta (Facebook/Instagram) click identifier. | | `msclkid` | String | | Microsoft Ads (Bing) click identifier. | | `ttclid` | String | | TikTok Ads click identifier. | | `twclid` | String | | Twitter/X Ads click identifier. | | `li_fat_id` | String | | LinkedIn Ads click identifier. | | `rdt_cid` | String | | Reddit Ads click identifier. | | `page_url` | String | | Full URL of the page. | | `page_path` | String | | Path component of the URL. | | `page_title` | String | | Title of the page. | | `library_name` | String | | Name of the SDK used to capture the event. | | `library_version` | String | | Version of the SDK used to capture the event. | | `browser` | String | | Name of the browser (e.g., chrome, firefox, safari). | | `screen_width` | Number | | Width of the device screen in pixels. | | `screen_height` | Number | | Height of the device screen in pixels. | | `screen_density` | Number | | Pixel density of the device screen (devicePixelRatio). | | `viewport_width` | Number | | Width of the browser viewport in pixels. | | `viewport_height` | Number | | Height of the browser viewport in pixels. | ## Timestamps Every API call has four timestamps: `original_timestamp`, `timestamp`, `sent_at`, and `received_at`. 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` property that's automatically collected by client-side SDKs. ### Timestamp overview | Name | Calculated / Value | | ------------------- | ----------------------------------------------------------------------------------------------------------------------------------- | | original\_timestamp | Time on the client device when call was invoked OR The timestamp value manually passed in through server-side libraries. | | sent\_at | Time on client device when call was sent OR sent\_at value manually passed in. | | received\_at | Time on Formo server clock when call was received | | timestamp | Calculated by Formo to correct client-device clock skew using the following formula: `received_at - (sent_at - original_timestamp)` | ### Original Timestamp The `original_timestamp` tells you when call was invoked on the client device or the value of timestamp that you manually passed in. > Note: The `original_timestamp` timestamp is not useful for any analysis since it's not always trustworthy as it can be easily adjusted and affected by clock skew. ### Sent At The `sent_at` timestamp specifies the clock time for the client's device when the network request was made to the Formo API. For libraries and systems that send batched requests, there can be a long gap between a datapoint's timestamp and sent\_at. Combined with `received_at`, Formo uses `sent_at` to correct the `original_timestamp` in situations where a user's device clock cannot be trusted (mobile phones and browsers). The `sent_at` and `received_at` 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 `sent_at` timestamp is not useful for any analysis since it's tainted by user's clock skew. ### Received At The `received_at` timestamp is added to incoming messages as soon as they hit the API. It's used in combination with `sent_at` to correct clock skew, and also to aid with debugging libraries and systems that deliver events in batches. ### Timestamp The `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. Formo automatically generates `timestamp` and you cannot manually set one directly in the call payload. Formo calculates timestamp as `timestamp = received_at - (sent_at - original_timestamp)`. ## Sample Event Here's an example event with common and contextual fields included: ```json theme={null} { "type": "page", "channel": "web", "version": "0", "project_id": "d5naNbBlqxSBXLuNa6zwc", "session_id": "117b982a451dc22edea6413b8e20958216c0a5b3baaa1d90699c42dbf4e74e33", "anonymous_id": "c2bc0ebe-d852-49d1-9efd-e45744850ae0", "user_id": "a46e6878-1ed5-4a81-9185-83608df2fcb6", "address": "0x8e6ca77a7e044ba836a97beb796c124ca3a6a154", "event": "FooBar", "context": { "user_agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/132.0.0.0 Safari/537.36", "locale": "en-US", "location": "ID", "timezone": "Asia/Saigon", "referrer": "https://chatgpt.com/", "ref": "vitalik.eth", "utm_source": "chatgpt.com", "utm_medium": "linkedin", "utm_campaign": "early-access", "utm_term": "", "utm_content": "", "page_url": "https://app.morpho.org/vaults/1", "page_path": "/vaults/1", "page_title": "USDC Vault | Morpho", "library_name": "Formo Web SDK", "library_version": "1.30.1", "browser": "chrome", "screen_width": 1920, "screen_height": 1080, "screen_density": 1, "viewport_width": 1920, "viewport_height": 969 }, "properties": { "name": "USDC Vault", "category": "Vaults", "url": "https://app.morpho.org/vaults/1?utm_source=chatgpt.com", "path": "/vaults/1", "hash": "#deposit", "title": "USDC Vault | Morpho" }, "message_id": "48555101eee2f44ac0f0632fcb7c7c9f6ce0012ae395ae79f8a0d515e4f5e41f", "original_timestamp": "2025-04-03 18:21:00", "sent_at": "2025-04-03 18:21:00", "received_at": "2025-04-03 18:21:00", "timestamp": "2025-04-03 18:21:00" } ```