Docs / Introduction

What is CHP?

Capability Host Protocol is a public boundary for exposing, invoking, governing, and auditing hosted capabilities.

Plain English

CHP helps independent systems agree on what can be done, who hosts it, who may call it, and what happened.

Why it exists

Agents, applications, and infrastructure providers need a shared contract that survives provider, runtime, and policy changes.

Formal definition

CHP standardizes manifests, discovery, invocation envelopes, lifecycle state, permission checks, structured outcomes, evidence, replay, and conformance.

Concrete example

Ground the concept before the schema.

A field-service company exposes schedule_technician as a hosted capability that an agent can discover and request under manager approval.

schedule_technicianInvokable

Finds an available qualified technician and reserves a service window.

host: ServiceOpsHostpolicy: approval_requiredv1.0.0

Policy boundary

Approval required

manager_approval

A manager must approve technician scheduling before the host returns a confirmed appointment.

Invocation trace

  1. 01 Actor

    Planning Agent

  2. 02 Capability

    schedule_technician

  3. 03 Host

    ServiceOpsHost

  4. 04 Policy

    manager_approval

  5. 05 Context

    job_context

  6. 06 Result

    Confirmed Appointment

manifest.json
json
{  "id": "service-ops-host",  "version": "0.1.0",  "protocol_version": "0.1",  "kind": "service",  "capabilities": [{    "id": "schedule_technician",    "version": "1.0.0",    "description": "Finds an available qualified technician and reserves a service window.",    "status": "experimental",    "modes": ["sync"],    "emits": ["execution_started", "execution_completed", "execution_denied"],    "policy": {      "risk_tier": "high",      "auth_required": true,      "approval_required": true,      "allowed_actors": ["agent://planning-assistant"]    },    "metadata": {      "required_permissions": ["service:dispatch"],      "lifecycle": "invokable"    }  }],  "evidence": {    "store": "local-append-only",    "append_only": true  }}

Relationships

Where this sits in the protocol.

Each concept should explain its neighbors so implementation teams can preserve the boundary across manifests, invocation, evidence, and tests.

Capabilities are the named abilities.

Hosts own lifecycle, policy, invocation, and evidence.

Conformance proves independent implementations behave consistently.

Visual model

  1. 01Actor discovers a host manifest.
  2. 02Actor invokes a compatible capability.
  3. 03Host returns a result or structured protocol outcome.

Implementation notes

  • Start with one real capability boundary.
  • Model denial and unavailable paths before trusting the happy path.
  • Use evidence and correlation IDs from the first implementation.

Common mistakes

  • Positioning CHP as only an agent tool schema.
  • Skipping policy and lifecycle states in early examples.
  • Treating logs as a substitute for protocol evidence.

Related concepts

Keep reading through the boundary.

Capability →Host →CHP vs MCP tools →