uhp

The Unified Harness Protocol in one import.

   your product ──▶ UHP ──▶ ┌── Codex
                            ├── Claude Code
                            ├── Hermes
                            └── the harness that ships next year

A harness is a complete agent runtime — a loop that plans, calls tools, edits files and reports back. Each one already knows how to do the work; what none of them agree on is how a product should drive one. UHP answers that once: how to start a task, follow its progress, continue the conversation, cancel it, get the files it produced, and understand why it failed.

UHP is not a model API and does not replace one. A model API gives you a turn: messages in, tokens out, tools you have to run yourself. UHP gives you a task: work in, and a running agent that uses its own tools, keeps its own session, and hands back results and files.

pip install uhp

Use it

import os
from uhp import connect

client = connect("http://localhost:3000", os.environ["UHP_API_KEY"])

harness = client.harnesses()[0]
for event in client.stream("Summarise README.md", harness_id=harness["id"]):
    if event["type"] == "response.output_text.delta":
        print(event["delta"], end="", flush=True)

Ask a server what it is before handing it a credential — discovery is unauthenticated by design:

from uhp import probe

probe("http://localhost:3000")
# {'protocol': 'uhp', 'versions': ['2026-08-11'], 'conformance_class': 'full', 'capabilities': {...}}

What's in the box

This package is the front door. It re-exports three focused ones so a caller needs a single dependency:

connect() returns that client; UhpClient is the same class under the protocol's name.

CLI

export UHP_BASE_URL=http://localhost:3000
export UHP_API_KEY=…

uhp discover
uhp harnesses
uhp stream "Summarise README.md" --harness chrn_…

It does not require anyone's cloud

UHP is an HTTP contract. A conformant server is any server that answers the requests in the specification with the responses in the specification — in containers, in subprocesses, on a queue, or on someone else's infrastructure. Nothing in the wire format requires a hosted service, an account, a licence key, or a call home. A client written against the specification works with any implementation that passes the conformance suite.

Specification

https://github.com/HarnessRouter/harnessrouter/tree/main/protocol

Apache-2.0.