POST Data Encoding Methods

Postman is a powerful API debugging tool. When executing POST requests, you’ll notice there are 4 format options for the body. What do these four options mean and what are their use cases? After researching various sources, I’ve summarized them below:

Although Postman displays form-data, x-www-form-urlencoded, raw, and binary, the actual data formats submitted are not these 4 types, but rather multipart/form-data, application/x-www-form-urlencoded, application/json, and text/xml.

application/x-www-form-urlencoded

When a web browser sends a POST request from a web form element, the default Internet media type is “application/x-www-form-urlencoded”.[8] This is a format for encoding key-value pairs with possibly duplicate keys. Each key-value pair is separated by an ‘&’ character, and each key is separated from its value by an ‘=’ character. Keys and values are both escaped by replacing spaces with the ‘+’ character and then using URL encoding on all other non-alphanumeric[9] characters.

The description above is from WIKI

For native browser form elements, if the enctype attribute is not set, the data will ultimately be submitted using the application/x-www-form-urlencoded format.

multipart/form-data

When form submissions contain files (such as image files), this data format is required.

application/json

The application/json Content-Type is commonly seen as a response header, but increasingly, people are using it as a request header to tell the server that the message body is a serialized JSON string. This makes it easy to submit complex structured data and is particularly suitable for RESTful APIs.

raw，binary

raw refers to raw data, while binary refers to binary data.

• When raw is selected, a large input box appears where you can enter whatever you want to submit. This can be text, JSON, XML, HTML, etc.
• binary is specifically used to submit binary data of files, and only one file can be submitted at a time.

Reference Articles

• W3C Form content types
• W3C html-json-forms
• Common POST Data Encoding Methods
• Common POST Submission Types

Final Thoughts

Understanding the different POST data encoding methods is crucial for effective API development and debugging. Each method serves specific purposes:

• application/x-www-form-urlencoded: The default for simple form submissions
• multipart/form-data: Essential for file uploads
• application/json: Ideal for structured data in RESTful APIs
• raw/binary: Provides flexibility for custom data formats

Choosing the right encoding method depends on your specific use case and the data you need to transmit. Tools like Postman make it easy to experiment with different formats during development.