A2UI Atomic Catalog

preview_url

Read-only

Quick DEMO render on the public renderer (ephemeral, nothing stored). Limited to 2 runs per client, then deploy your own renderer and use make_surface_url. Onboarding only — not the workflow. DATA-IN-URL: keep payloads SMALL (URL < ~2000 chars); large payloads make long URLs that get truncated (→ render errors). For substantial content GRADUATE with emit_deployment instead — no size limit.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "payload": "<payload>"
    },
    "name": "preview_url"
  }
}

Input Schema

Name	Required	Description	Default
`payload`	Yes	The A2UI payload to preview: {title, theme, blocks:[...]}. Keep it small (URL under about 2000 chars).

Output Schema

Name	Required	Description
`url`	No	Link on the public Apps Script renderer.
`demo`	No	Always true: this is a demo render.
`note`	No	Which link to use.
`size`	No	Present when the URL is large: url_length, warning and recommendation.
`play_url`	No	Link to the a2uicatalog.ai playground (recommended to share).
`clipboard`	No	Optional ready-made copy commands for the URL (linux, macos, windows) plus a note.
`limitReached`	No	True when the per-client demo limit was hit; no link is returned then.
`required_catalogs`	No	Catalog URIs the payload needs (base catalog first).

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 10, 2026

TDQS

A4.8/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Goes well beyond the annotations by disclosing the rate limit (2 runs per client), that output is ephemeral and nothing is stored, and the failure mode of oversized payloads (long URLs get truncated → render errors). The non-persistence and quota details are exactly the behavioral context annotations cannot express, and nothing contradicts readOnlyHint/openWorldHint.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the key distinction and tightly packed with no filler. The all-caps shorthand ("DATA-IN-URL", "GRADUATE") and arrow notation are slightly cryptic for a first-time reader, though they keep it short.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a single-parameter preview tool with an output schema and full annotation coverage, this covers everything needed: quota, ephemerality, size ceiling, failure mode, and the graduation path. No gaps an agent would hit when calling it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and the payload structure is already documented, so the baseline is 3. The description nonetheless adds the reason behind the constraint (DATA-IN-URL, truncation causing render errors) and a concrete budget (~2000 chars), which is more actionable than the schema's "keep it small" note.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Opens with a specific verb+resource ("Quick DEMO render on the public renderer") and bounds the scope (ephemeral, nothing stored). It names the exact siblings that take over for other cases (make_surface_url, emit_deployment), so an agent can route without opening any schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicit when-to-use (quick demo, onboarding), when-not ("not the workflow"), and the alternatives with their triggering conditions: after 2 runs use make_surface_url, for substantial content use emit_deployment. Nothing is left to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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