UHPUHP Developer Guide
Independent resource · Not affiliated with HarnessRouter · Last verified 15 Aug 2026
Home / What Is UHP? Unified Harness Protocol Explained
Concepts

What is the Unified Harness Protocol (UHP)?

UHP is an open execution protocol for products that want to run complete agent harnesses through a consistent interface rather than integrate every harness separately.

Verified: Protocol: 2026-08-11No executable JS

Direct definition

The Unified Harness Protocol (UHP) defines how a client drives a complete agent harness through a UHP server. The protocol is concerned with execution: choosing a configured harness, sending a task, observing progress, continuing related work, exchanging files, cancelling execution, receiving structured failures and collecting final output.

In the current specification, a harness is the complete agent runtime around a model. That runtime can own an agent loop, tools, skills, session state and a working environment. UHP intentionally does not prescribe how that harness is built internally.

The integration problem UHP tries to solve

Complete coding and agent harnesses expose more than a model-completion endpoint. They maintain conversation state, run tools, manipulate files, stream intermediate events, enforce limits and produce artifacts. A product integrating several harnesses would otherwise need a separate adapter for each runtime and would inherit each runtime's lifecycle semantics.

UHP attempts to move that variability behind one contract:

Product / CLI / CI job
        │
        │  UHP over HTTP
        ▼
     UHP server
        │
        ├── Codex
        ├── Claude Code
        └── Hermes

The server may use containers, subprocesses, queues or remote workers internally. Those implementation details are outside the protocol and should not leak into the client's wire format.

What UHP standardizes

  • Protocol-version negotiation and capability discovery.
  • Harness discovery and, at the Full class, harness lifecycle management.
  • One-shot and streaming task execution.
  • Session continuation and session inspection where supported.
  • Cancellation and terminal task states.
  • File input, artifacts and downloads at higher conformance classes.
  • Authentication and object scoping requirements.
  • A machine-readable error model.

The current version uses date-based version identifiers. The published version is 2026-08-11.

What UHP is not

It is not a model API. UHP drives a harness, not raw inference. It is not MCP. MCP standardizes the boundary between an AI application and external tools, resources and prompts. It is not a harness configuration file format. A separate project called Harness Protocol focuses on portable harness.yaml configuration.

Do not infer vendor adoption from examples. The UHP specification uses stable harness-base strings such as codex, claude-code and hermes, and HarnessRouter Community Edition supports those backends. That is different from OpenAI, Anthropic or Nous Research independently implementing UHP.

Current status

As of 15 August 2026, UHP is an open protocol initiated and led by HarnessRouter. Its repository contains a versioned specification, OpenAPI 3.1 and JSON Schema artifacts, a runnable conformance suite, governance documents and a reference implementation.

The protocol is technically concrete but ecosystem adoption is still early. The key signal to watch is independent implementation: another server passing the conformance suite, or a major harness vendor publicly adopting the protocol.

Read next

Continue with UHP architecture, then read UHP vs MCP if you are deciding where the protocol fits in an existing agent stack.

Primary sources