# 400: URL Anatomy (Path vs Query Parameters)

## What This Guide Is For

This is a detailed guide for `400 BAD REQUEST` errors caused by incorrect URL construction.

If you are troubleshooting a `400 BAD REQUEST`, use the dedicated guide:
- [400: Bad Request](https://www.marketdata.app/docs/api/troubleshooting/bad-request)

## Introduction to URL Parameters

URL parameters (query strings) pass optional input to an endpoint after the path.

### URL Anatomy: Path vs Query String

A URL with parameters has the following structure:

<pre>
https://<span class="url-host">api.marketdata.app</span>/<span class="url-path">v1/stocks/quotes/SPY/</span>?<span class="url-query">token=token1234&dateformat=timestamp</span>
</pre>

- **Protocol**: `https://`
- **Host**: <span class="url-host">`api.marketdata.app`</span>
- **Path (or Endpoint)**: <span class="url-path">`/v1/stocks/quotes/SPY/`</span>
- **Query String**: Begins with a `?` and includes <span class="url-query">`token=token1234&dateformat=timestamp`</span>
  - `token` and `dateformat` are the names of the parameters.
  - `token1234` and `timestamp` are the values assigned to those parameters.
  - `&` is used to separate multiple parameters.

### What Goes In The Path

- Required route values like symbols, ids, or endpoint-specific path parts.
- Example: `/v1/stocks/quotes/SPY/`

### What Goes In The Query String

- Optional controls like `token`, `dateformat`, `limit`, and similar parameters.
- Query values always use `key=value` form.
- Multiple parameters are separated by `&`.

## How to Build URL Parameters

When building URL parameters, follow these guidelines to ensure they are structured correctly:

1. **Start with the Endpoint URL**: Identify the base URL of the API endpoint you are interacting with.
2. **Add a Question Mark**: Follow the base URL with a `?` to start the query string.
3. **Append Parameters**: Add parameters in the format `key=value`. Use `&` to separate multiple parameters.
4. **Encode Special Characters**: Use URL encoding to handle special characters in keys or values.

### Example

Suppose you want to request stock quotes for `SPY` with a specific date format and token authentication:

```
https://api.marketdata.app/v1/stocks/quotes/SPY/?token=token1234&dateformat=timestamp
```

### Common Mistakes

- **Incorrect Character Usage**: Ensure you use `?` to start and `&` to separate parameters.
- **Unencoded Characters**: Encode special characters like spaces (`%20`), plus (`%2B`), etc, using URL encoding.