HITL Protocol Interactive Playground
HITL v0.9 Draft — illustrative local playground; all data and outcomes are simulated
HITL v0.9 Draft — illustrative local playground; all data and outcomes are simulated
A review URL grants access to one case. It does not identify a person. When policy requires a named reviewer, the service authenticates and authorizes that reviewer before revealing protected content or accepting a response.
The first accepted response is immutable. A correction uses a new case linked with previous_case_id. A timeout default does not count as human approval or verification.
completed records the review response. Business execution requires independent current authorization. Optional Agent Access v0.1 adds prepare → authenticated owner review → fresh commit.
GET poll_url every 30s–5min, respecting Retry-After and ETag where offered. Stateless. No server needed on agent side. Works everywhere.events_url. Server pushes status updates. Reconnect or fall back to the authenticated poll endpoint. No public agent endpoint needed.callback_url. Requires agent to expose a public endpoint. Signed via X-HITL-Signature: sha256=<hmac> header. Correlate the case, authenticate delivery and deduplicate retries.previous_case_id chain)context.form. Supports multi-step wizards.OpenClaw agent finds jobs for a user. Two HITL rounds: select jobs, then record whether to send applications. Actual sending requires separate authorization.
Claude Code (CLI agent) builds v2.1.0. CI/CD service needs human sign-off before production deploy.
CMS agent drafts a blog post. Editor reviews, requests changes, agent revises. Chain of linked review cases.
DevOps agent negotiates infrastructure budget via ADL. Platform policy triggers human approval via HITL bridge.
Service needs structured data from the human — form fields, validation, conditional visibility, and optional multi-step wizard flows.
Email service needs confirmation before sending. Agent renders native messaging buttons — the human explicitly chooses an action. Service policy may require a browser step-up.
Proof-of-human evidence and reviewer identity are separate checks.
How HITL core compares to adjacent standards and optional declarative UI companions. The browser review URL remains the canonical fallback. This is a scoped comparison, not a protocol ranking. MCP 2026-07-28 form / URL modes ↗; long-running tasks are an optional extension.
| Feature | HITL | AG-UI | A2UI | Adaptive Cards | MCP Form / URL | Slack Blocks |
|---|---|---|---|---|---|---|
| URL-based delivery | Yes | No | No | Partial | URL mode | No |
| Browser fallback is core | Yes | No | No | Partial | URL mode | No |
| Async (hours/days) | Yes | No | No | No | Tasks extension | No |
| Rich forms | Yes | Yes | Yes | Partial | External URL | Partial |
| State/data separation | Minimal | Embedded | Yes | No | Mode dependent | No |
| No platform lock-in | Yes | No | Yes | Yes | Yes | No |
| Open standard | Yes | Yes | Yes | Yes | Yes | No |
| CLI agent support | Yes | No | No | Partial | Yes | No |
| Mobile support | Yes | Partial | Partial | Yes | Client dependent | Yes |
| Crypto signing | Partial | No | No | No | No | No |
| Real-time updates | Yes | Yes | Yes | No | Tasks / client | Yes |
| Multi-round chains | Yes | No | No | No | No | No |
| Delegation + audit | Yes | No | No | No | No | No |