Llama.Grammar

Llama.Grammar is a C# class library that allows you to define JSON Schemas, C# objects dynamically and convert them to GBNF (Grammar-Based Next-Token Format) grammars. It is useful for working with structured outputs in AI models like LLaMA, Mistral, or GPT when paired with inference runtimes that support GBNF grammars.

Features

• 🧱 Fluent builder API for creating JSON Schema objects in C#
• 🧠 Converts JSON Schema to GBNF
• ✅ Supports complex schema features like:
  • Nested objects
  • Arrays and array constraints
  • Enums and constants
  • Required fields
  • Pattern matching
  • Nullable types

Installation

Add the library to your project:

dotnet add package Llama.Grammar

Usage

Generating GBNF using fluent API

You can create JSON Schemas using the fluent API and convert them to GBNF grammars. Here's an example of how to do this

using Llama.Grammar.Helper;
using Llama.Grammar.Service;

var schemaBuilder = new SchemaBuilder()
    .Type("object")
    .Properties(p => p
        .Add("name", s => s.Type("string"))
        .Add("age", s => s.Type("integer"))
        .Add("nicknames", s => s.Type("array")
                                    .MinItems(1)
                                    .MaxItems(3)
                                    .Items(i => i.Type("string"))))
    .Required("name", "age");

string json = schemaBuilder.ToJson();

IGbnfGrammar grammar = new GbnfGrammar();
var gbnf = grammar.ConvertJsonSchemaToGbnf(json);
Console.WriteLine(gbnf);

Generating GBNF from C# Types

You can generate GBNF grammars directly from C# types, including nested objects and collections

public class TestPerson
{
    public string Name { get; set; } = string.Empty;
    public int Age { get; set; }
    public List<string> Nicknames { get; set; } = new();
    public Address? HomeAddress { get; set; }
}

public class Address
{
    public string Street { get; set; } = string.Empty;
    public string City { get; set; } = string.Empty;
    public string? ZipCode { get; set; }
}

IGbnfGrammar grammar = new GbnfGrammar();
var gbnf = grammar.ConvertTypeToGbnf<TestPerson>();
Console.WriteLine(gbnf);

Based on

This project is based on the excellent work by Adrien Brault, porting and wrapping his TypeScript logic for use in .NET.

License

MIT License. See LICENSE. for details.