> ## Documentation Index
> Fetch the complete documentation index at: https://docs.requestly.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Run Collections with Custom Data
> Learn how to use CSV or JSON data files with the Requestly Collection Runner to iterate requests with multiple input values.
You can use **custom data files** (CSV or JSON) when running a collection manually in Requestly.\
This enables you to iterate through your requests using multiple sets of input values, without modifying your request parameters each time.
**Note:** This feature is currently available only on the [Requestly Desktop App](https://requestly.com/downloads/desktop/).
Use this feature to test APIs with dynamic inputs, such as running the same workflow for multiple users, IDs, or configurations.
### Using a Data File in Collection Runner
Follow these steps to run a collection with custom data:
In the Collections sidebar, find the collection you want to execute and click the **Run** icon next to it.
In the Runner configuration panel, click **Select Data File**.
Supports JSON & CSV files (max 100MB)
Once added, Requestly will automatically detect the file type and preview its structure.
After selecting the file, a **preview** of your data will appear.
* For CSV files: verify column names and types
* For JSON files: check object keys and structure
Each key or column name should match the variable used in your requests, such as `{{storyId}}`.
Click **Save** and then **Start Run**.\
The Collection Runner will replace variables with data from your file for each iteration.
### How Data Files Work
When you attach a CSV or JSON file to your manual run:
* Each **row (CSV)** or **object (JSON)** represents one **iteration**
* Variables inside your requests (like `{{storyId}}`) will be replaced with the corresponding values
* Requestly automatically cycles through each data set until all iterations are complete
### Supported File Formats
#### CSV Format
* The first row defines variable names
* Each subsequent row represents one iteration
* Each row must have the same number of columns
**Example:**
```bash theme={null}
city,temperature
Vancouver,10
Austin,24
London,12
```
#### JSON Format
* Must be an array of key-value objects
* Each object defines one iteration
**Example:**
```json theme={null}
[
{ "city": "Vancouver", "temperature": 10 },
{ "city": "Austin", "temperature": 24 },
{ "city": "London", "temperature": 12 }
]
```
### Example Use Case
For a request like
```bash theme={null}
GET https://api.example.com/weather?city={{city}}
```
and a data file containing
```bash theme={null}
city
Vancouver
Austin
London
```
Requestly will automatically replace `{{city}}` with each value during the run.
### Accessing Data in Scripts
You can access data file values programmatically in your pre-request and post-response scripts using the `rq.iterationData` object. This allows you to implement conditional logic, validate responses, or perform calculations based on the input data.
**Example:**
```javascript theme={null}
// Pre-request script
const city = rq.iterationData.get("city");
console.log(`Testing weather API for: ${city}`);
// Post-response script
const expectedCity = rq.iterationData.get("city");
const responseData = rq.response.json();
rq.test("Response contains correct city", function() {
rq.expect(responseData.city).to.equal(expectedCity);
});
```
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Once added, Requestly will automatically detect the file type and preview its structure.
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