Scalar types represent leaf values in a GraphQL response. GraphQL provides five built-in scalar types:

• Int — a signed 32-bit integer.
• Float — a signed double-precision floating-point value.
• String — a UTF-8 character sequence.
• Boolean — true or false.
• ID — an identifier intended to be serialized as a string.

Example:

type Product {
  id: ID!
  name: String!
  quantity: Int!
  price: Float!
  available: Boolean!
}

A scalar is a leaf because the client cannot select fields beneath it.

For example:

product {
  name
  price
}

is valid, but this is not:

product {
  price {
    value
  }
}

because Float has no child fields.

ID versus String

An ID represents an identifier. It is commonly used for database identifiers and resource identifiers. Although GraphQL serializes IDs in a string-compatible way, using ID communicates semantic intent: this value identifies something.

Integer versus Float

Use Int for whole numbers and Float for decimal numbers. Be careful with financial data: a GraphQL Float should not automatically be interpreted as an appropriate representation for exact monetary calculations. Production financial systems often use decimal representations at the application or database layer.