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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and non-open-world, so the safety profile is fully covered. The description does add one genuinely useful behavioral fact beyond the annotations — the output is a 0-100 score benchmarked 'against ideal bands' — but it never says how the bands are defined, how the three signals are weighted, or what happens when values fall far outside the bands.

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?

The core purpose and output shape are front-loaded in a single efficient sentence. The trailing promotional link to an external calculator site is the one sentence that does not earn its place for an agent deciding whether to call the tool.

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 only three required numeric inputs, full schema coverage, no output schema and a complete read-only annotation set, the remaining burden on the description is small. Disclosing the 0-100 output range covers the main gap; ideal-band thresholds would be nice but are not strictly required to invoke it 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 description coverage is 100%, so all three parameters (fontSizePx, lineHeight multiplier, lineLengthChars) are already documented in the schema. The description restates the same three dimensions without adding units, valid ranges, or units-of-measure guidance beyond what the schema provides, so 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?

States a specific verb and resource: 'Score body copy legibility' on three named dimensions, producing a 0-100 score. That is clear enough to distinguish it from most siblings, though it never names the nearest neighbors (cta_visual_hierarchy_tester, ux_pattern_anti_pattern_checker) or states what makes this different from them.

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?

There is no when-to-use guidance, no prerequisites, and no mention of alternatives. The only routing signal is an external URL for a 'full version', which points outside the toolset rather than to a sibling tool.

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