Open Source Universal Agent API

One API for Every AI Agent

Write your agent code once and run it on any harness — Anthropic SDK, Goose, LangChain, Letta, and more. Stop rewriting integrations. Start building.

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The Problem

Every AI agent harness has its own API, its own patterns, its own quirks.

Rewrite integration code for each harness
Learn different APIs, types, and conventions
Vendor lock-in makes switching painful
No way to compare harnesses objectively

The Solution

Open Harness provides a single, unified API that works across all major agent harnesses.

Write once, run on any supported harness
Consistent API for execution, tools, memory
Switch harnesses with a one-line change
Compatibility matrix shows real capabilities

Get Started in Seconds

Python TypeScript

from openharness_anthropic_agent import AnthropicAgentAdapter
from openharness.types import ExecuteRequest

# Create adapter - swap this line to switch harnesses
adapter = AnthropicAgentAdapter(api_key="...")

# Same code works with any adapter
async for event in adapter.execute_stream(ExecuteRequest(message="Hello!")):
    if event.type == "text":
        print(event.content, end="")
      