Harness Context Protocol
The open standard for installing capabilities into any agent harness. Skills teach the agent, MCP connects it to tools, and HCP installs the capability.
One pack runs two loops on any harness.
Harness Context Protocol (HCP) defines how an agent harness installs a capability. The unit is a versioned Harness Pack that a runtime can lint, authorise, bind to credentials, sandbox, and execute. Whether the request comes from a terminal, an agent, an API, or a UI button, it runs as the same command.
A pack is a directory with three files. It describes an existing CLI (or API), says what each command is allowed to do, and teaches an agent how to use it. It contains no secrets and requires no server.
packs/transit/
surface.json manifest: id, adapter, Binding mode, named commands
policy.json rules: read|write, land, confirm, per command and per trigger
HARNESS.md Skill: one screen that teaches the hot pathChoose your path
Build a pack
Wrap a CLI you already have. Copy a gold pack, change four fields, lint, exec.
Implement a runtime
Load packs, enforce grants, mint Binding, sandbox the adapter, report availability.
Adopt in a host
Give your agent product native pack intake, with the same ease as adding an MCP server.
Read the specification
Normative requirements, schemas, and conformance checklists for packs, runtimes, and hosts.
Learn the model
What is HCP?
The one-page answer, and where it sits beside Agent Skills, MCP, and Agent Plugins.
Architecture
Execute and Sense: two isolated loops on one pack, sharing Policy and Binding.
Design principles
The twelve rules every conforming pack, runtime, and host follows.
Concepts
Pack, command, Policy, Binding, Sense, Skill, Adapter, Principal, Invoker, runtime.
Go deeper
Pack classes
Five shapes to copy: public read, gated write, linked channel, emit-only, control.
Authorization
Principals, privacy lands, five capability grants, and what fails closed.
CLI reference
Every hcp command, its JSON output, exit codes, and the local store.
Roadmap
What HCP/1.1 ships, what HCP/1.2 and HCP/2 add, and how to propose changes.
For agents
This site is readable by machines as well as people. Every page is available as
Markdown at /api/md/<path>; the whole corpus is at /llms.txt and
/llms-full.txt; search is at /api/search?query=.