Hello, sorry to be spammy but I love working on JSV, my JSON Schema Validator library.
This is a small release with three important things:
Module-based schemas now need to export a json_schema/0 function instead of a schema/0 function. This makes more sense since we are starting to export json_schemas from other modules like Ecto schema modules. A generic schema/0 function is confusing in that case. Codebases using the old callback will still work, but a warning will be emitted.
Example:
defmodule ItemModule do
def json_schema do
%{type: :string}
end
end
schema = %{type: :array, items: ItemModule}
data = ["foo", "bar"]
Modules using JSV.defschema/1 will automatically export the new function as well as the old one, with a deprecation warning.
That defschema macro now supports passing the properties as a list directly.
So instead of this:
defmodule MyApp.UserSchema do
use JSV.Schema
defschema %{
type: :object,
properties: %{
name: %{type: :string},
age: %{type: :integer, default: 0}
}
}
end
You can do this:
defmodule MyApp.UserSchema do
use JSV.Schema
defschema name: %{type: :string},
age: %{type: :integer, default: 0}
end
And because use JSV.Schema imports the new schema definition helpers, it can be as short as this:
defmodule MyApp.UserSchema do
use JSV.Schema
defschema name: string(),
age: integer(default: 0)
end
Finally, I’ve added the defschema/3 macro that works like defschema/1 but also defines a module:
defmodule MyApp.Schemas do
use JSV.Schema
defschema User,
name: string(),
age: integer(default: 0)
defschema Admin,
"""
With a schema description and @moduledoc
""",
user: User,
privileges: array_of(string())
end
I think it’s nice to have this when defining some responses schemas directly in controllers or message queue consumers, à la Pydantic.
And that’s it Thanks for reading!
[0.10.0] - 2025-07-10
Features
Define and expect schema modules to export json_schema/0 instead of schema/0
Allow to call defschema with a list of properties
Added the defschema/3 macro to define schemas as submodules
Bug Fixes
Ensure defschema with keyword syntax supports module-based properties
Looking at you files it appears those are LLM generated right? I think it did a pretty good job (though it should have stopped at some point in that test guide, at the end it’s making things up). What did you use?
I tried to use Exdantic with JSV but we have an incompatibility. JSV expects raw data with binary keys while Exdantic seem to expect atom keys only:
Mix.install([
{:jsv, "~> 0.10"},
{:exdantic, "~> 0.0.2"}
])
defmodule UserSchema do
use Exdantic, define_struct: true
schema "User account information" do
field :name, :string do
required()
min_length(2)
description("User's full name")
end
field :email, :string do
required()
format(~r/^[^\s@]+@[^\s@]+\.[^\s@]+$/)
description("Primary email address")
end
field :age, :integer do
optional()
gt(0)
lt(150)
description("User's age in years")
end
field :active, :boolean do
default(true)
description("Whether the account is active")
end
# Cross-field validation
model_validator(:validate_adult_email)
# Computed field derived from other fields
computed_field(:display_name, :string, :generate_display_name)
config do
title("User Schema")
strict(true)
end
end
def validate_adult_email(input) do
if input.age && input.age >= 18 && String.contains?(input.email, "example.com") do
{:error, "Adult users cannot use example.com emails"}
else
{:ok, input}
end
end
def generate_display_name(input) do
display =
if input.age do
"#{input.name} (#{input.age})"
else
input.name
end
{:ok, display}
end
use JSV.Schema
def json_schema do
JSV.Schema.with_cast([__MODULE__, :from_jsv])
end
defcast from_jsv(data) do
validate(data)
end
def format_error("from_jsv", [exdantic_error | _], _) do
Exdantic.Error.format(exdantic_error)
end
end
root = JSV.build!(UserSchema) |> dbg()
data = %{"name" => "alice", "email" => "foo@bar.com"}
JSV.validate!(data, root)
I just used Claude Code. Yeah, Claude likes being “helpful”, whether hallucinating ideas or running git reset --hard after you ask it to not lose uncommitted work! (!!)
Thanks for looking at that integration doc with JSV. It was just brainstorms, really. Will look when time allows.
Thanks for reading!
Features
Bug Fixes
