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

Annotations already declare readOnlyHint and openWorldHint, but the description adds substantial extra context: it is a public API needing no credentials, it normalizes underscores to hyphens, it resolves Material Symbols to the outlined variant with a filled fallback, and it fully describes how the SVG must be plumbed into Webcake (svgMask per breakpoint, color from styles.background, preserveAspectRatio='none'). That is real behavioral disclosure beyond the structured hints.

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 and API reference, then progressive detail on formats, resolution rules, return shape, and Webcake rendering. Every clause carries information, though the Webcake rendering passage is dense enough that the paragraph runs long.

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 single-parameter tool with no output schema, the description compensates by documenting the return shape ({ icons: { '<ref>': { ok, svg, iconify } } }) and the downstream rendering contract. An agent has everything needed to call it and consume the result correctly.

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 100%, so the baseline is 3, but the description goes further by defining the transformation semantics of each ref string — prefix handling, underscore-to-hyphen conversion, and bare-name treatment as Material Symbols. It adds meaning the schema example alone does not convey.

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 (resolves) and resource (icon-font names into inline SVG markup) and names the concrete backing service (public Iconify API). It is unmistakable against siblings like search_images or render_preview because it operates on icon refs, not images or pages.

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?

Explains the accepted ref formats ('ms:verified', 'fa:chart-line', 'mdi:home', bare names) and ties them to where the agent will encounter them (block.icon values from an ingest result), which is clear contextual guidance. It stops short of explicitly stating when-not to use it or naming a fallback alternative, so it lands just under full marks.

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