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Table of Contents
Which values ??will be considered "empty"?
Nested structures are also applicable
What if you want to customize it?
Home Backend Development Golang How to ignore empty fields in golang json marshaling

How to ignore empty fields in golang json marshaling

Jul 07, 2025 am 12:25 AM

In Go's JSON serialization, empty fields can be ignored through the omitempty option of the json tag. 1. Usage method: Add omitempty to the json tag of the structure field, such as json:"age, omitempty"; 2. Values ??that are considered "empty" include: 0 of the numeric type, "" of the string, false of the boolean, nil pointer, arrays, slices, maps and structs with length 0 or completely empty; 3. Note: When the boolean value is false, it will be ignored, and even if the pointer points to a zero value, it will not be ignored; 4. Omitempty is also applicable to nested structures; 5. Custom requirements can be handled by implementing the json.Marshaler interface. The rational use of omitempty can improve the quality of JSON output and reduce the amount of data transmission.

How to ignore empty fields in golang json marshaling

During Go's JSON serialization process, if you want to ignore empty fields in the structure (such as zero values ??or nil ), there is actually a very straightforward way: use the omitempty option of the json tag. This avoids passing meaningless default values ??to the receiver, especially when communicating with front-end or other services.

How to ignore empty fields in golang json marshaling

Ignore empty fields using omitempty

Go's standard library encoding/json supports adding omitempty to the json tag of structure fields. As long as the field is "empty" (such as 0 , "" , nil , false , etc.), the field will not appear in the final JSON output.

How to ignore empty fields in golang json marshaling

For example:

 type User struct {
    Name string `json:"name"`
    Age int `json:"age,omitempty"`
    Email string `json:"email,omitempty"`
}

If you create a User instance:

How to ignore empty fields in golang json marshaling
 u := User{Name: "Alice"}

The output JSON will be:

 {
  "name": "Alice"
}

Age and Email fields that are not set are automatically ignored.


Which values ??will be considered "empty"?

omitempty does not just determine whether it is nil , it has its own set of rules to determine whether the field is empty:

  • Numeric type (int, float): zero value (0, 0.0) will be ignored
  • String : empty string "" is ignored
  • Boolean value : false will be ignored (note this!)
  • Pointer : Pointer to zero value will not be ignored (for example, new(int) points to 0) but nil pointer will be ignored
  • Array, slice, map, struct : will be ignored only if the length is 0 or all fields are empty

Therefore, you should pay special attention when using it. For example, after adding omitempty to the Boolean field, it will also be filtered out when the value is false , which may not be the result you want.


Nested structures are also applicable

If your structure contains nested structures or pointers, you can also use omitempty normally:

 type Address struct {
    City string `json:"city,omitempty"`
    Zip string `json:"zip,omitempty"`
}

type User struct {
    Name string `json:"name"`
    Address *Address `json:"address,omitempty"`
}

If Address is nil or the fields inside are empty, the entire address field will be ignored.


What if you want to customize it?

If your needs are more complex, such as if some fields are kept even if they are empty, or if you decide whether to serialize a certain field based on business logic, you cannot simply rely on omitempty . At this time, you can consider implementing the json.Marshaler interface to customize the output logic.

However, for most cases, it is enough to use omitempty well.


Basically that's it. Using omitempty rationally can make your JSON output cleaner and reduce unnecessary data transmission. But remember to pay attention to its behavioral boundaries, especially the boolean and zero values.

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