---
title: "span_start_timestamp"
url: https://develop.sentry.dev/sdk/foundations/transport/event-payloads/properties/span_start_timestamp/
---

# undefined

* `start_timestamp`

  *Required*. A timestamp representing when the measuring started. Theformat is either a string as defined in [RFC3339](https://tools.ietf.org/html/rfc3339) or a numeric (integer or float)value representing the number of seconds that have elapsed since the [Unixepoch](https://en.wikipedia.org/wiki/Unix_time). The `start_timestamp` value must be less than orequal to the `timestamp` value, otherwise the Span is discarded as invalid.

```json
{
  "start_timestamp": "2011-05-02T17:41:36.242Z"
}
```

or:

```json
{
  "start_timestamp": 1304358096.242
}
```