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

Annotations already establish this as a safe read (readOnlyHint=true), so the bar is lower. The description still adds real behavioral value beyond the annotations: it discloses that the environment validates markup and rejects naive Tailwind/HTML output, which tells the agent this is effectively a prerequisite rather than an optional reference.

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?

Purpose and scope are front-loaded in the first sentence, with the usage directive second; nothing is wasted on filler. The second sentence is slightly long, but both clauses (the trigger and the reason) carry information, so the length is largely earned.

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?

There is no output schema, but the description compensates by summarizing the guide's contents (dialect, component set, discarded style, complete worked example). An agent knows exactly what it will receive and when it must call it, so nothing needed to invoke or interpret the tool 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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline for a no-param tool is 4. Schema coverage is 100% anyway, and no argument details are needed or missing.

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?

Specific verb ('Get') plus precisely scoped resource ('the guide to authoring a wireframe mockup'), and it enumerates what the guide contains (markup dialect, component set, discarded style, full example). It is clearly distinguishable from sibling tools like get-mockup and create-mockup, which operate on actual mockups rather than on authoring guidance.

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?

Gives an explicit trigger — 'Call this BEFORE composing your first mockup in a conversation' — and states the consequence of skipping it (markup written from general Tailwind/HTML habits is refused). This is a textbook when-to-use directive with the alternative behavior and its failure mode spelled out.

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