unifiedharnessprotocol

The Unified Harness Protocol, as data.

A harness is a complete agent runtime — a loop that plans, calls tools, edits files and reports back. UHP is the HTTP contract for driving one: start a task, follow it, continue the conversation, cancel it, collect the files it produced.

This package contains no network code. It is the specification's vocabulary in machine-readable form, so that a client, a server, or a test suite can agree on the strings without each one retyping them out of the prose and getting one subtly wrong.

pip install unifiedharnessprotocol

from unifiedharnessprotocol import (
    PROTOCOL_VERSION, Events, TaskStatus, ERROR_CODES,
    is_terminal, is_retryable, check_discovery, check_sequence,
)

PROTOCOL_VERSION                          # '2026-08-11'
is_terminal(TaskStatus.IN_PROGRESS)       # False
is_retryable(code="quota_exhausted")      # False — nothing changes until the quota does

What's in it

Two checks worth running

Does the server's class claim match its capabilities? A class claim that contradicts the capability list tells a client two different things, and it is cheap to notice.

import json, urllib.request
from unifiedharnessprotocol import check_discovery

with urllib.request.urlopen("http://localhost:3000/v1/uhp") as response:
    ok, problems = check_discovery(json.load(response))

Did the stream drop an event? sequence_number starts at 0 and increases by exactly 1. That rule exists so a client can tell a lost event from a quiet agent — but only if it checks.

check_sequence(events)     # (False, [7, 8])

Related

• harnessclientprotocol — SSE decoding, output assembly, idempotency keys and retry policy
• harnessrouter — the HTTP client and CLI
• uhp — all three under one import

Specification

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

Apache-2.0.