# Developing a Custom Formatter

Source: https://revive.run/docs/formatter

This app works best with JavaScript enabled.HomeDocsRulesGuidesDevelop ruleDevelop formatterAPIDeveloping a Custom Formatter
Each formatter needs to implement the following interface:
type Formatter interface {
Format(<-chan Failure, RulesConfig) (string, error)
Name() string
}
The Format method accepts a channel of Failure instances and the configuration of the enabled rules. The Name() method should return a string different from the names of the already existing rules. This string is used when specifying the formatter when invoking the revive CLI tool.
Example
Let us implement a sample formatter which outputs the rule failures to plain text.
First, you need to clone the repository and create a file under revive/formatter called sample.go. After that, add the following imports and struct declaration:
package formatter
import (
"fmt"
"github.com/mgechev/revive/lint"
)
type Sample struct {
Metadata lint.FormatterMetadata
}
Now, Sample has to implement the Formatter interface, which means that we need to define two methods: Name which returns the name of the formatter, and the method Format. As a first argument Format receives a channel where we'll receive the failures, and as second argument the method accepts the user's configuration.
func (f *Sample) Name() string {
return "sample"
}
// Format formats the failures gotten from the lint.
func (f *Sample) Format(failures <-chan lint.Failure, _ lint.RulesConfig) (string, error) {
for failure := range failures {
fmt.Printf("%v: %s\n", failure.Position.Start, failure.Failure)
}
return "", nil
}
In the implementations above, Name returns the string "sample" and Format prints the failures one by one, first displaying the failure's position and after that its description.