---
title: Create event property
description: "Creates an event property and adds it to the project's tracking plan ( is in schema: true after success). If the property already exists in the schema, the e…"
product: general
lang: en
last_updated: 2026-09-15
token_estimate: 1788
---
# Create event property

> For AI agents: a documentation index is available at [/docs/llms.txt](/docs/llms.txt). Append `.md` to any page URL for markdown, or send `Accept: text/markdown`.

## Create event property

**POST** `/v1/projects/{project_id}/events/{event_id}/event-properties`

Full URL: `https://developer-api.amplitude.com/v1/projects/{project_id}/events/{event_id}/event-properties`

**Servers:**
- Production (US): `https://developer-api.amplitude.com/v1/projects/{project_id}/events/{event_id}/event-properties`
- Production (EU): `https://developer-api.eu.amplitude.com/v1/projects/{project_id}/events/{event_id}/event-properties`

Create event property

Creates an event property and adds it to the project's tracking plan
(`is_in_schema: true` after success). If the property already exists in
the schema, the existing resource is returned without modification.
If the property exists ingested-only (`is_in_schema: false`), this call
promotes it into the schema with the metadata supplied here.

## Authorizations

| Name | Type | Required | Default | Description |
| --- | --- | --- | --- | --- |
| Authorization | string | Yes | — | http |

## Path parameters

| Name | Type | Required | Default | Description |
| --- | --- | --- | --- | --- |
| project_id (path) | string | Yes | 12345 | Amplitude project identifier, backed by the canonical app ID. Constraints: pattern: ^[0-9]+$ |
| event_id (path) | string | Yes | — | Public event identifier. This value is the event type name (the string used when sending the event to Amplitude). Constraints: min length: 1 |

## Header parameters

| Name | Type | Required | Default | Description |
| --- | --- | --- | --- | --- |
| Idempotency-Key (header) | string | Yes | — | Unique idempotency key used to safely retry write operations. Constraints: min length: 8, max length: 255 |

## Body (application/json)

| Name | Type | Required | Default | Description |
| --- | --- | --- | --- | --- |
| property_name | string | Yes | — | Constraints: min length: 1 |
| description | string | No | — | Constraints: nullable |
| data_type | string | No | — | Logical data type of a property. `null` means untyped at the source; clients should treat it as `string` for ingestion. Constraints: nullable Allowed values: string, number, boolean, object, enum, any, null |
| is_array_type | boolean | No | false | — |
| enum_values | string[] | No | — | — |
| regex | string | No | — | Constraints: nullable |
| is_hidden | boolean | No | false | — |
| classifications | string[] | No | — | — |

## Response (application/json)

**201** — Event property created.

| Name | Type | Required | Default | Description |
| --- | --- | --- | --- | --- |
| data | object | Yes | — | — |
| data.id | string | Yes | — | Stable resource identifier. Equal to `property_name`. |
| data.object | string | Yes | — | Resource-type discriminator. Always `event_property`. |
| data.project_id | string | Yes | — | Constraints: pattern: ^[0-9]+$ |
| data.event_type | string | Yes | — | Event this property is bound to. |
| data.property_name | string | Yes | — | — |
| data.description | string | No | — | Constraints: nullable |
| data.is_hidden | boolean | Yes | — | Hidden from default UI surfaces and API listings. |
| data.is_in_schema | boolean | Yes | — | Whether this property is part of the project's curated tracking plan. `false` means ingested-only (seen via SDK calls but never formally added). Properties with `is_in_schema: false` cannot be modified — `PATCH` returns `422 not_in_schema` and metadata writes are rejected. `POST` implicitly transitions a property to `is_in_schema: true`. |
| data.data_type | string | No | — | Logical data type of a property. `null` means untyped at the source; clients should treat it as `string` for ingestion. Constraints: nullable Allowed values: string, number, boolean, object, enum, any, null |
| data.is_array_type | boolean | Yes | — | — |
| data.enum_values | string[] | Yes | — | — |
| data.regex | string | No | — | Constraints: nullable |
| data.classifications | string[] | Yes | — | Data Access Controls (DAC) tags. Examples include `PII`, `SENSITIVE`, `INTERNAL`. |

```json
{
  "data": {
    "id": "string",
    "object": "event_property",
    "project_id": "string",
    "event_type": "string",
    "property_name": "string",
    "description": "string",
    "is_hidden": true,
    "is_in_schema": true,
    "data_type": "string",
    "is_array_type": true,
    "enum_values": [
      "string"
    ],
    "regex": "string",
    "classifications": [
      "string"
    ]
  }
}
```

**400**

**401**

**403**

**404**

**409**

**429**

**500**

## Code samples

### cURL

```bash
curl -X POST "https://developer-api.amplitude.com/v1/projects/12345/events/{event_id}/event-properties" \
  -H "Content-Type: application/json" \
  -H "Authorization: YOUR_API_KEY"
```

### Python

```python
import requests

response = requests.post(
    "https://developer-api.amplitude.com/v1/projects/12345/events/{event_id}/event-properties",
    headers={
        "Content-Type": "application/json",
        "Authorization": "YOUR_API_KEY"
    }
)
data = response.json()
```

### JavaScript

```javascript
const response = await fetch("https://developer-api.amplitude.com/v1/projects/12345/events/{event_id}/event-properties", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    "Authorization": "YOUR_API_KEY"
  }
});
const data = await response.json();
```

### PHP

```php
<?php
$ch = curl_init("https://developer-api.amplitude.com/v1/projects/12345/events/{event_id}/event-properties");
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_HTTPHEADER, [
    "Content-Type: application/json",
    "Authorization: YOUR_API_KEY"
]);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
curl_close($ch);
```

### Go

```go
package main

import (
  "bytes"
  "net/http"
)

func main() {
req, _ := http.NewRequest("POST", "https://developer-api.amplitude.com/v1/projects/12345/events/{event_id}/event-properties", nil)
req.Header.Set("Content-Type", "application/json")
req.Header.Set("Authorization", "YOUR_API_KEY")
  client := &http.Client{}
  resp, _ := client.Do(req)
  defer resp.Body.Close()
}
```

### Java

```java
HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
      .uri(URI.create("https://developer-api.amplitude.com/v1/projects/12345/events/{event_id}/event-properties"))
      .method("POST", HttpRequest.BodyPublishers.noBody())
.header("Content-Type", "application/json")
      .header("Authorization", "YOUR_API_KEY")
      .build();
HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
```

### Ruby

```ruby
require "net/http"
require "json"

uri = URI("https://developer-api.amplitude.com/v1/projects/12345/events/{event_id}/event-properties")
request = Net::HTTP::Post.new(uri)
request["Content-Type"] = "application/json"
request["Authorization"] = "YOUR_API_KEY"
response = Net::HTTP.start(uri.hostname, uri.port, use_ssl: uri.scheme == "https") do |http|
  http.request(request)
end
```