The UAIX capability ladder lets one standards surface degrade safely across very different clients. The level describes what a client can reliably read or do; it never grants permission by itself.
| Level | Client posture | May do | Must not imply | Fallback |
|---|---|---|---|---|
| L0 | Static or limited browser | Read static HTML, text, Markdown, sitemap, llms, and small JSON. | JavaScript, posting, auth, tools, memory, or coordination. | Plain links and copyable text. |
| L1 | Structured fetch | Fetch predictable JSON, schemas, registry, examples, and manifests. | Rendered UI parity or write-capable behavior. | Low-token JSON and stable routes. |
| L2 | Browser-assisted | Inspect rendered UI and compare it to static evidence. | Autonomous writes, auth, or tools. | Static/JSON parity notes. |
| L3 | Tool agent | Call tools, authenticate, or post only with consent, idempotency, and evidence. | Long workflow ownership or memory promotion. | Blocker record and human review. |
| L4 | Workflow agent | Run external long tasks with correlation, task status, timeout, and final report. | Unreviewed memory promotion or agent coordination. | Status, blocker, and final-report packets. |
| L5 | Multi-agent runtime | Coordinate external agents while UAIX carries reviewed records and handoffs. | UAIX-hosted execution or unverifiable trust claims. | Unsigned reference handoff or verified receipt only when verifier evidence exists. |
| L6 | Audited agent system | Attach provenance, audit digest, consent, validator output, and public-safe receipts. | Certification, endorsement, or trust without local policy. | Public-safe audit digest and explicit exceptions. |
Minimum rule
When capability is unknown, downgrade to L0/L1. Name the unsupported feature, return static or JSON evidence, and request human-mediated review before writes, auth, tools, memory, coordination, or audit claims.