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

Annotations already cover the safety profile (readOnly, non-destructive, closed-world). The description adds genuinely useful behavioral context beyond them: the entire catalog is returned in a single response, and the call does not count toward usage limits, which affects how aggressively an agent should avoid repeating it.

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?

A single tightly-packed sentence front-loads the core verb and scope, then tacks on the caching and quota caveats. No filler, no restatement of the title or annotations.

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 input parameters and no output schema, the description carries the burden of explaining what comes back, and it does: grouped-by-category sets with prefix, name, and icon count, plus the reuse and quota behavior. An agent has everything needed to call this correctly and cache the result.

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 the baseline is 4; there is no parameter syntax for the description to compensate for. The description instead documents the shape of the returned entries (prefix, name, icon count), which is a reasonable substitute given no output schema exists.

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 (List) and resource (every hosted icon set) and even previews the return shape (grouped by category, with prefix, name, icon count). This cleanly distinguishes it from siblings get_icon and search_icons, which operate on individual or queried icons rather than enumerating the catalog.

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?

"Call it once per conversation and reuse the result" gives clear operational context for when to invoke it, and the catalog-enumeration framing implies it precedes per-icon lookups. However, it never explicitly names get_icon or search_icons as the follow-up alternatives, so the routing guidance is implicit rather than stated.

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