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

With no annotations, the description carries the full burden and does so: accepted formats, base64 transport, content-digest storage, the exact pinned shape ({mediaType, contentDigest, source: uploaded}), revision bumping, and the returned baseRevision. It even discloses failure-mode behavior (a key whose bytes a lane cannot show renders a placeholder rather than erroring), which is unusually rich.

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

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

Front-loaded with the core action, then constraints, then ordering and idempotency. Dense but nearly every clause earns its place; only the placeholder-rendering sentence is arguably extra, and even that prevents a wrong error-handling assumption.

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

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

An output schema exists, so return-value detail is not required, yet the description still calls out baseRevision for the caller to quote. Combined with ordering rules, idempotency, and registry-refusal behavior, nothing needed to invoke this correctly is missing.

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

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

Schema coverage is 75%, so most params are documented structurally, but the description adds real meaning: which image formats are accepted for `imageBase64`, how it is encoded, and the implicit limit is echoed from the schema. The `token` param is left entirely to the schema, which is a minor gap but acceptable given header-preference is already explained there.

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

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

The description opens with a concrete verb+resource: put image bytes behind an `assetKey` so an `asset/image` node renders it. It explicitly distinguishes this from `ui_builder_apply`, which inserts the node that consumes the key, so an agent can tell the two apart without opening schemas.

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

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

It states the required ordering ('Put the picture first, then insert the `asset/image` node with ui_builder_apply') and the reason the reducer will refuse a key that is neither pinned nor in the catalog registry. It also names the idempotency condition (same bytes under same key change nothing), which is exactly the when-to-call/when-it-is-a-no-op guidance an agent needs.

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