Custom Errors in Go (Custom Error)


Although error messages may not be the flashiest or most motivating thing to see in development, they play a vital role in helping determine the next course of action and, more importantly, in preventing programs from terminating prematurely. Let's stop from.

In Go, like any other programming language, errors provide mechanisms to anticipate and deal with potentially unexpected situations while providing helpful and meaningful feedback to the user.

Fortunately, in Go, we have access to a ton of tools and features for effective error handling. However, you may find instances where the built-in error messages and features don't meet your actual app needs.

This is where custom errors come into play. As the name suggests, custom errors allow us to define precise and specific information for error messages that match the application.

In this tutorial, we'll walk you through the process of setting up custom errors in Go, explain why you might need them, and explore examples of how to work with custom errors.

Basics of Error Handling

Before we learn how to create and use custom errors in Go, let's understand the basics of error handling in Golang.

Go presents errors using the error interface. The Error interface has a single method called Error() string. Any type that implements this method allows Go to treat it as an error.

Here, take a look at the following example code:

package main
Import ,



funk divide,a,b int, ,in terror, ,
If B== 0 ,
return,“Division by zero”,
return A , B, zero
main work,, ,
result, error := divide,10, 0,
If to make a mistake ,= zero ,

In the given example, we use the error.New() function which allows us to create a new error with a descriptive message when trying to divide by zero.

golang custom errors

As the name suggests, custom errors are basically user-defined error types that implement the Error interface. The role of custom errors is to allow us to create error objects with custom fields and behavior. This helps provide more context and specificity in the error message to enhance error handling.

use custom errors

You might be wondering why you need custom error types when you can use basic logging techniques using the built-in features.

While the built-in error types are more than sufficient for a wide range of cases, custom error types have several advantages such as:

  1. Clear context – Custom errors provide an additional layer of context about the error making it easier to understand and debug. Some additional information about custom errors includes the function where the error occurred, any relevant data associated with it, and more.
  2. Type Safety – Since custom errors are themselves types, they allow us to define methods on them that allow us to create a structured and type-safe error handling logic.
  3. Encapsulation – Custom errors allow us to encapsulate specific domain rules which can lead to a cleaner code.

Create custom error type

To create custom errors in Go, we basically need to define our own custom error types that implement the Error interface.

The following shows the basic structure of defining a custom error in Go:

Type custom error structure ,
message string
code int
Celebration ,I ,custom error, Mistake,, string ,
return e-message

In the example code given, we define a custom error type called “CustomError” with the error code “Msg” as the field for the message and “Code” as an integer.

Then we invoke the Error() method on “CustomError” which returns the error message.

Finally, we can create a custom error using this error type as shown in the following example:

work work,, Mistake ,
return ,custom error,Message: “something went wrong”Code: 42,

Use custom errors in Go

Once we create custom errors, we can use them in code just like any other built-in error.

The following example shows how to use the “custom error” that we defined in the previous step:

main work,, ,
error := func,,
If to make a mistake ,= zero ,
If Mistake, right := mistake.,,custom error,, Ok ,
fmt.printf,“Custom error: %s (code: %d)\n,error message, error code,
, Other ,
fmt.println,“general error:”mistake,
, Other ,
fmt.println,“No error occurred.”,

In the given example, we call a function called “func” and check if it returns any error. If it does, we use a Golang type assertion to check whether it is of type “CustomError”. If this is true, we access the “Message” and “Code” custom fields.


In this tutorial, we taught you everything you need to know about custom errors in Go. We learned about the Error interface, the error() method, how to implement it, how to create a custom error type and how to use custom error types.

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By Ranjan