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IDL · CBOR · Multi-target Codegen · Schema Stability

Define Once,
Generate Everywhere

IonPath is a contract language and binary protocol for distributed applications. Write .ion schemas, generate type-safe C# and TypeScript code, and enforce wire-format stability with schema locks.

Get Started Documentation
example.ion 
msg User {
  id: u4;
  name: string;
  email: string?;
  roles: u4[];
}

service UserService(spaceId: u4) {
  GetUser(userId: u4): User;
  CreateUser(name: string, email: string?): User;
  stream WatchUpdates(): User;
}
27+
Primitive Types
CBOR
Binary Protocol
3
Target Languages
30+
Diagnostic Codes
Capabilities

Everything you need for typed contracts

From schema definitions to production-ready, type-safe code in C# and TypeScript.

Rich IDL Syntax

Messages, services, unions, enums, flags, generics, typedefs, and custom attributes. Everything to describe your domain precisely.

Syntax Overview →

CBOR Encoding

Compact binary serialization using CBOR. Index-based field encoding for maximum wire efficiency — like protobuf, but with richer type support.

Wire Protocol →

Multi-target Codegen

Generate type-safe code for C# (.NET) and TypeScript (browser) from a single .ion source.

Code Generation →

Schema Locks

Pin field indices, method signatures, and enum values in ion.lock.json. Breaking changes are detected at compile time.

Schema Lock →

Streaming RPC

Unary request-response and full-duplex streaming over WebSocket. Ticket-based authentication built in.

Services →

Comprehensive Diagnostics

30+ error codes with cycle detection, typo suggestions via Levenshtein distance, and schema migration warnings.

Diagnostics →

JavaScript SDK

Browser-ready TypeScript SDK with binary reader/writer, CBOR codec, and formatter system. Works with generated service clients.

JS SDK →

.NET Runtime

Server and client libraries for ASP.NET Core. DI integration, interceptors, OpenTelemetry instrumentation, and deadline handling.

.NET Runtime →

VS Code Extension

Syntax highlighting for .ion files, JSON schema validation for ion.config.json, and TextMate grammar.

Getting Started →
Get Started

Three steps to your first contract

1

Install the CLI

Install ionc as a .NET global tool:

dotnet tool install -g ionc
2

Write your schema

Create a .ion file with your types and services:

msg User {
  id: u4;
  name: string;
  email: string?;
  roles: u4[];
}

service UserService(spaceId: u4) {
  GetUser(userId: u4): User;
  CreateUser(name: string, email: string?): User;
  stream WatchUpdates(): User;
}
3

Compile

Run the compiler to generate code and lock the schema:

$ ionc init
→ Created ion.config.json

$ ionc compile
→ Compiled 3 modules (C#, TypeScript)
→ ion.lock.json updated
Full Getting Started Guide
Learn

Documentation

Comprehensive guides for every aspect of IonPath.

Getting Started

Install ionc, write your first .ion file, compile.

Language Reference

Messages, services, unions, enums, generics, and more.

Primitive Types

27+ types with C# and TypeScript mappings.

Compiler

CLI commands, flags, pipeline stages.

Schema Lock

Prevent breaking changes with ion.lock.json.

JavaScript SDK

Browser-ready SDK with CBOR and formatters.

.NET Runtime

Server and client libraries for ASP.NET Core.

Code Generation

What ionc generates for C# and TypeScript.

Diagnostics

All ION error codes with causes and fixes.