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Table of contents
The Issue With Input Validation
Creating Informative Error Messages
Working with Validations in Gin
Improving Error Messages
Frequently Asked Questions
What is Gin?
Why is Gin used for input validation in APIs?
How does Gin handle input validation?
Can I customize the error messages returned by Gin?
Can I create my custom validators in Gin?
Last Updated: Mar 27, 2024

Input Validation for API's using Gin

Author Amit Singh
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Prerita Agarwal
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23 Jul, 2024 @ 01:30 PM


Have you worked with the Go programming language? Have you ever worked on the Gin framework in the Go programming language?


This article focuses on one of the frameworks of the Go programming language, i.e., Gin. We will study the issue with input validation in detail. We will try to understand how to create good error messages as well. We will also see validation in Gin and many other concepts.

The Issue With Input Validation

Similar to validating a user's form input, a quality API makes sure that any data sent to it (such as request bodies, query parameters, and HTTP headers) has the correct content and format. If it doesn't, it gives the user or developer helpful feedback to encourage them to make the necessary adjustments.

Unfortunately, if an API returns any error messages, they are frequently not very helpful. At worst, you might get a straightforward HTTP 500 error that vaguely says, "something went wrong." Even APIs that do a decent job of validating user input and returning HTTP 404 status codes when anything goes wrong, however, frequently need help with clear error messages. So simply validating the incoming data is insufficient. The finest APIs deliver helpful messages that allow the caller to correct their errors and move on swiftly.

Fortunately, the high-speed Go-powered API framework gin-gonic/gin makes use of the well-liked go-playground/validator module and enables you to define validation directly in your struct tags. It takes more work to configure these validators, extend or alter them, and produce helpful errors. The amount and complexity of the documentation on this topic could be more extensive and easier to comprehend.

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Creating Informative Error Messages

There are as many perspectives about the data that APIs should return as there are APIs. While some APIs promote user feedback and openness, others can identify security or privacy considerations that must be carefully considered and have an impact on the amount of material that can be returned. However, there are a few characteristics that well-designed APIs typically have in common.

When there is any problem, the users generally have the following questions:

  1. What exactly happened? 
  2. Where did it happen?
  3. Why did it happen?
  4. When did it go wrong?
  5. Who is going to suffer?

We can presume that the answers to the When and Who questions are obvious when discussing input validation only. When providing validation feedback, it should be quick and focused on the question "When." They should only have an effect on the person who has submitted the input. Therefore, the API response only has to provide responses to the first three queries.

The HTTP response code should include an explanation of what went wrong. For example, an HTTP 400 response code indicates that the data was transmitted but was invalid, and the response body contains information on "where" and "why" the error occurred. You can decide how to respond to these inquiries. You can use simple solutions like returning a predictable, parsable response in the following format:

“The field ‘firstName’ is mandatory and cannot remain empty”


You can also make it more complicated.

firstName: {  validation: “required”,  message: “cannot be empty” }

Working with Validations in Gin

You should ensure that request validation is straightforward, maintainable, and scalable since it is something you should ideally perform for each endpoint. Fortunately, Gin includes a built-in framework for validating structs that uses go-playground/validate under the scenes. As a result, you can practically configure all the validation scenarios by using straightforward struct tags, and gin will automatically carry out that validation during request unmarshalling.

If you're already familiar with go-validate, you'll note that gin won't pick it up unless you use the 'binding' tag rather than the 'validate' tag. In addition, you can also use the go-validate engine to include unique validation functions. It truly supports all the same validation directives aside from that.

When you call "MustBind," "ShouldBind," or any of their derivatives, Gin will do data validation if a "binding" struct tag is present. It's crucial to remember that marshaling comes first, so if there is a marshaling problem (for example, if the time cannot be parsed or if a string rather than an int is put in), validation will not take place. You will receive a "json.MarshallingTypeError" or "time.ParseError" instead.

Improving Error Messages

In case you want to create more human-readable error messages in Go, you can use the go-playground translation libraries or manually parse and construct custom messages. Gin returns "validator.ValidationErrors" containing information about fields that did not pass validation, why they did not pass, and the specific parameters used in the validation. This allows you to create validation messages in any desired format.

To further improve the error messages, you can use additional switch statements to create clear and understandable messages for each validation tag in use. By doing this, you can change the output to a more user-friendly series of messages.

Frequently Asked Questions

What is Gin?

Gin is a web framework for the Go programming language.

Why is Gin used for input validation in APIs?

It is commonly used for input validation in APIs because it provides a convenient and flexible way to validate incoming requests and ensure that only valid data is processed.

How does Gin handle input validation?

Gin uses a library called "validator" to handle input validation. This library allows you to specify validation rules for different fields in a request, and it will automatically check that the incoming data meets these rules. If the data is not valid, Gin will return an error indicating which field or fields failed validation.

Can I customize the error messages returned by Gin?

Yes, you can customize the error messages returned by Gin by manually parsing and constructing your own messages or using the go-playground translation libraries. You can also use additional switch statements to create clear and understandable messages for each validation tag in use.

Can I create my custom validators in Gin?

You can create your custom validators in Gin and add the tags to the function called parseError to generate a comprehensive set of error messages. This allows you to extend the validation capabilities of Gin and tailor it to the specific needs of your API.


In this article, we have studied one of the frameworks of the Go programming language, i.e., Gin. We have studied the issue with input validation in detail. We have understood how to create good error messages as well. We have also seen validation in Gin.

We hope that this article has provided you with the help to enhance your knowledge regarding the Gin framework and if you would like to learn more, check out our articles on gin rest api and test with swagger openapi and gin setting up a json web token jwt.

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