Specification
Harness Context Protocol HCP/1.1, the normative requirements for packs, runtimes, and hosts. Status, conformance language, and table of contents.
This is the Harness Context Protocol specification, HCP/1.1, in the draft of
17 September 2026. Its text lives in the spec/ directory of the
protocol repository,
and the Specification pages on harnesscontextprotocol.io are generated from it.
Changes land there by RFC.
Status and version#
This document specifies HCP/1.1. It consists of the HCP/1 core plus the accepted extensions of RFC 0001 (wrap hardening) and RFC 0003 (wrap exec plane), with the errata of RFC 0008. Packs, runtimes, and hosts claiming conformance to HCP/1.1 MUST implement or follow the requirements in the sections below.
HCP/1 packs conform to HCP/1.1 without change. Proposed and planned changes are tracked on the Roadmap and are not part of this specification.
Conformance language#
The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this specification are to be interpreted as described in RFC 2119 and RFC 8174 when, and only when, they appear in all capitals.
Text marked informative explains intent and does not create requirements.
Three conformance targets#
| Target | Claims conformance by | Checklist |
|---|---|---|
| Pack | Passing lint on a conforming runtime | Pack conformance |
| Runtime | Passing the conformance vectors and satisfying the runtime checklist | Runtime conformance |
| Host | Loading generated surfaces and satisfying the host checklist | Host conformance |
Table of contents#
| § | Section | Defines |
|---|---|---|
| 1 | Terminology | The objects and their exact meanings |
| 2 | Pack model | Directory, three files, identity, planes, invariants |
| 3 | Manifest | surface.json schema and validation |
| 4 | Policy | policy.json schema, tokens, coverage, confirm |
| 5 | Skill | HARNESS.md requirements |
| 6 | Execute | Envelope, pipeline, wrap rendering, result |
| 7 | Sense | Triggers, isolation, activation |
| 8 | Binding | Modes, hubs, families, mint, health |
| 9 | Authorization | Principal, scope, capabilities, evaluation order, audit |
| 10 | Sandbox | Default posture and native-local |
| 11 | Lifecycle | States, store, availability |
| 12 | Projections | CLI face, host surfaces, MCP export naming |
| 13 | Versioning | Protocol affinity, compatibility, deprecation |
| 14 | Conformance | Checklists for packs, runtimes, hosts |
Design goals (informative)#
- A capability installs into any harness as one portable unit.
- Authorisation, credentials, sandboxing, and outbound events are part of the install layer; no host adds them separately.
- The same command serves a human, an agent, an API, and a UI under one Policy.
- Packs are small to write and cannot hold secrets.
- Runtimes may be proprietary; the format and rules are open.
- Transports are projections. A pack's identity does not depend on its transport.
Non-goals#
See Non-goals.
License#
The specification is licensed under Apache-2.0. The reference SDK and CLI are MIT.