# Dynamic Variables

> Inject dates, timestamps, UUIDs, and environment variables into payload and expected files at runtime.

Source: https://docs.ktestify.xyz/docs/write-tests/dynamic-variables

KTestify processes **dynamic variable placeholders** in file content before sending or comparing. This lets you inject runtime values (current date, random IDs, environment-specific data) into your test payloads and expected files without hardcoding them.

All file reads go through `FileUtils.getFileContent()`, which transparently resolves placeholders before returning content.

---

## Syntax

Placeholders use the form `{{TYPE:format}}` or `{{TYPE}}`:

```json
{
  "orderId":   "{{RANDOM:UUID}}",
  "createdAt": "{{DATE:yyyy-MM-dd}}",
  "updatedAt": "{{TIMESTAMP:epoch}}",
  "envUser":   "{{ENV:CI_USER}}"
}
```

---

## Available variable types

### `{{DATE:format}}`

Current local date formatted with [`DateTimeFormatter`](https://docs.oracle.com/en/java/docs/java/time/format/DateTimeFormatter.html).

| Example | Output |
|---|---|
| `{{DATE:yyyy-MM-dd}}` | `2026-05-09` |
| `{{DATE:dd/MM/yyyy}}` | `09/05/2026` |
| `{{DATE:yyyyMMdd}}` | `20260509` |

---

### `{{TIMESTAMP:format}}`

Current UTC timestamp.

| Example | Output |
|---|---|
| `{{TIMESTAMP:epoch}}` | `1746748800000` (milliseconds since epoch) |
| `{{TIMESTAMP:yyyy-MM-dd'T'HH:mm:ss'Z'}}` | `2026-05-09T10:00:00Z` |

---

### `{{RANDOM:type}}`

Generates a random value.

| Example | Output |
|---|---|
| `{{RANDOM:UUID}}` | `f47ac10b-58cc-4372-a567-0e02b2c3d479` |
| `{{RANDOM:INT}}` | Random integer |

---

### `{{ENV:VARIABLE_NAME}}`

Reads a value from an environment variable at test runtime.

```json
{
  "targetHost": "{{ENV:TARGET_HOST}}",
  "apiKey":     "{{ENV:API_KEY}}"
}
```

If the environment variable is not set, the placeholder is left as-is (no error is thrown). Use this to parameterise tests across CI environments.

---

## Using dynamic variables in expected files

Dynamic variables work in **expected** files too, so you can assert against a computed value:

```json title="assets/expected/order-enriched.json"
{
  "orderId":   "order-001",
  "processedAt": "{{DATE:yyyy-MM-dd}}",
  "status":    "PROCESSED"
}
```

This means the assertion is date-aware without you having to update the file daily.

---

## Custom dynamic variables

To add your own variable type, implement `DynamicVariable` in `ktestify-core` and register it via `DynamicVariableFactory`. See [Extend → Core concepts →](../extend/core-concepts) for details.