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

readOnlyHint=true already covers the safety profile, so the description's added value is the disclosure that results include real shipped weights and a siteFonts list of already-installed families (which cost nothing extra). It does not mention pagination or result-size behavior, but it does add meaningful return context beyond the annotations.

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-loads the core purpose in the first sentence and keeps the routing advice tight. The trailing "Rules:" line is a slightly awkward tack-on but is short and actionable, so little is wasted.

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?

With no output schema, the description does supply the key return shape (matching families, their weights, and a siteFonts set). For a read-only search tool with four optional parameters this is nearly complete; only the undocumented limit/category behavior 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 description coverage is 50%: q and cyrillicOnly are documented in the schema, while limit and category are not. The description adds no parameter-level meaning at all (no mention of paging, result caps, or category filtering), so it fails to compensate for the undocumented half.

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?

States a specific verb (search) and resource (Google Fonts catalogue) plus a second scope (the fonts already installed on this site). It explicitly names the sibling save-design-system that consumes its output, so an agent can place it in the workflow without opening other 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?

Gives a concrete trigger ("Call it BEFORE naming a font in save-design-system") and a prerequisite (read get-skill-doc design-system-contract first). There is no explicit when-not-to-use guidance, but the sequencing instruction is clear enough to select the tool correctly.

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