Harmony

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Harmony is an Open Source & Models tool that provides a renderer for OpenAI's harmony response format, specifically for the gpt-oss model series. It offers consistent formatting and fast performance for defining conversation structures and generating reasoning output.

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At a glance

Pricing

Open Source

Free tier

Yes

API

Yes

Skill level

Technical

About

What is harmony?

Harmony is an open-source renderer developed by OpenAI for its harmony response format, designed to be used with the gpt-oss open-weight model series. This tool is crucial for developers building their own inference solutions for gpt-oss, as it ensures correct formatting for conversation structures, reasoning output, and structured function calls. It mimics the OpenAI Responses API, making it familiar to users of that API. Harmony enables models to output to multiple channels for chain of thought, tool calling preambles, and regular responses, supporting various tool namespaces and a clear instruction hierarchy. The library is built with Rust for performance and offers first-class Python support with `pip` installation and typed stubs.

Best used for

Ideal for developers and data scientists who need to implement custom inference solutions for OpenAI's gpt-oss models, define complex conversation structures, and ensure accurate reasoning and function call formatting. Especially valuable for maintaining consistent and loss-free token sequences in AI model interactions.

Common actions

render response format

define conversation structures

generate reasoning output

structure function calls

build inference solutions

open-sourceautomated workflowcollaborationdeepfakelow-code/no-code"AI Agents"workflowsface swappinggithub copilot

Capabilities

Key features

Consistent formatting
Fast performance
Python support
Rust core
Structured output
Multi-channel output

Target Audience

developerdata scientist

Integrations

Not yet documented

Pricing & Plans

Open Source

Free

FAQs

What is the primary purpose of OpenAI Harmony?

OpenAI Harmony is a renderer for the harmony response format, specifically designed for OpenAI's gpt-oss open-weight model series. Its main purpose is to ensure correct formatting for conversation structures, reasoning output, and structured function calls when building custom inference solutions.

Do I need Harmony if I'm using gpt-oss through an API or provider like HuggingFace?

No, if you are using gpt-oss through an API or a provider like HuggingFace, Ollama, or vLLM, you typically do not need to be concerned with Harmony. Your inference solution or provider will handle the necessary formatting automatically.

What programming languages does Harmony support?

Harmony is primarily built in Rust for performance, with first-class Python support provided through pyo3 bindings. This allows developers to use it efficiently in both Rust and Python environments, with installation available via pip for Python.

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