Working with JSON

Json values are supported through codecs which encode/decode values to json strings. However, third-party libraries are needed for actual json parsing/printing. Currently, Circe and µPickle are supported.


To use Circe add the following dependency to your project:

"com.softwaremill.tapir" %% "tapir-json-circe" % "0.9.3"

Next, import the package (or extend the TapirJsonCirce trait, see MyTapir):

import tapir.json.circe._

This will bring into scope Codecs which, given an in-scope circe Encoder/Decoder and a SchemaFor, will create a codec using the json media type. Circe includes a couple of approaches to generating encoders/decoders (manual, semi-auto and auto), so you may choose whatever suits you.

Note that when using Circe’s auto derivation, any encoders/decoders for custom types must be in scope as well.

For example, to automatically generate a JSON codec for a case class:

import tapir._
import tapir.json.circe._

case class Book(author: String, title: String, year: Int)

val bookInput: EndpointIO[Book] = jsonBody[Book]

Circe lets you select an instance of io.circe.Printer to configure the way JSON objects are rendered. By default Tapir uses Printer.nospaces, which would render

  "key1" -> Json.fromString("present"),
  "key2" -> Json.Null



Suppose we would instead want to omit null-values from the object and pretty-print it. You can configure this by overriding the jsonPrinter in tapir.circe.json.TapirJsonCirce:

object MyTapirJsonCirce extends TapirJsonCirce {
  override def jsonPrinter: Printer = Printer.spaces2.copy(dropNullValues = true)

import MyTapirJsonCirce._

Now the above JSON object will render as



To use µPickle add the following dependency to your project:

"com.softwaremill.tapir" %% "tapir-json-upickle" % "0.9.3"

Next, import the package (or extend the TapirJsonuPickle trait, see MyTapir and add TapirJsonuPickle not TapirCirceJson):

import tapir.json.upickle._

µPickle requires a ReadWriter in scope for each type you want to serialize. In order to provide one use the macroRW macro in the companion object as follows:

import tapir._
import upickle.default._
import tapir.json.upickle._

case class Book(author: String, title: String, year: Int)

object Book {
  implicit val rw: ReadWriter[Book] = macroRW

val bookInput: EndpointIO[Book] = jsonBody[Book]

Like Circe, µPickle allows you to control the rendered json output. Please see the Custom Configuration of the manual for details.

For more examples, including making a custom encoder/decoder, see TapirJsonuPickleTests.scala

Other JSON libraries

To add support for additional JSON libraries, see the sources for the Circe codec (which is just a couple of lines of code).


To create a json codec automatically, not only a circe Encoder/Decoder is needed, but also an implicit SchemaFor[T] value, which provides a mapping between a type T and its schema. A schema-for value contains a single schema: Schema field.

For custom types, schemas are derived automatically using Magnolia, given that schemas are defined for all of the case class’s fields. It is possible to configure the automatic derivation to use snake-case, kebab-case or a custom field naming policy, by providing an implicit tapir.generic.Configuration value:

implicit val customConfiguration: Configuration =

Alternatively, SchemaFor values can be defined by hand, either for whole case classes, or only for some of its fields. For example, here we state that the schema for MyCustomType is a String:

implicit val schemaForMyCustomType: SchemaFor[MyCustomType] = SchemaFor(Schema.SString)