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

Annotations already cover the safety profile (readOnly, non-destructive, closed-world), and the description adds genuinely new behavior: the widget renders live in chat, and in hosts without MCP Apps support the result degrades to a page address. It stops short of saying what the response looks like in the normal case (rendered artifact vs. text).

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?

Two short sentences, front-loaded with the primary behavior and followed by the fallback case; nothing redundant. The phrasing "the answer has the address of the widget page" is slightly awkward but not wasteful.

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?

For a simple one-parameter read tool with no output schema, the description covers both the primary outcome (live preview in chat) and the degraded outcome (URL to open), which is the key thing an agent needs to relay. Only the exact shape of the non-fallback result remains unstated.

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?

With a single parameter and 100% schema description coverage, the schema already defines widget_id and even its provenance (list_widgets). The description adds no further semantics about format or where to obtain the id, so the baseline 3 applies.

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?

"Shows the live widget in the chat, as it shows on a site" names a concrete verb (shows/previews) and resource (widget), and the live-rendering framing separates it from config-oriented siblings like get_widget or get_embed_code. It never names those siblings explicitly, so differentiation is inferred rather than stated.

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?

Usage is implied: the tool is for seeing how a widget looks, and the description notes what happens in environments without MCP Apps support. There is no explicit 'use this instead of get_widget/get_embed_code when…' guidance or stated prerequisite such as having a widget_id from list_widgets.

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