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

With no annotations, the description carries the full burden and does well: it discloses parallel fetching of both URLs, :root custom-property extraction, the Levenshtein <= 2 rename heuristic, no-browser execution, and ~24h per-URL-pair caching. It stops short of stating auth requirements, rate limits, or failure behavior when a URL is unreachable, so it is strong but not exhaustive.

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?

Content is front-loaded with the core purpose before the dimensions, alternatives, and return shape. The long inline JSON return listing is verbose, but since no output schema exists it earns most of its space; a few clauses could still be trimmed.

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, so the description takes on the job of enumerating return fields (score, grade, added[], renamed[], contrastDrift[], etc.), and it does so thoroughly alongside scope, exclusions, and caching semantics. Nothing an agent needs to invoke and interpret this 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?

Schema description coverage is 100% and both parameters already carry their own descriptions with examples ('your design system' / 'reference or competitor'), so the baseline is 3. The prose adds role framing ('live URLs') but no format or constraint detail beyond what the schema provides.

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?

The description opens with a specific verb+resource ('Diff two design systems from live URLs') and immediately differentiates itself by naming the mechanism ('URL-scoped design-token diff engine') and enumerating the 8 diff dimensions. An agent can distinguish this from designesy_drift_score and designesy_monitor_score without opening any schema.

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?

It gives explicit trigger phrasings ('what actually changed between two design systems') and an explicit 'When NOT to use' clause that routes single-site drift to designesy_drift_score and continuous monitoring to designesy_monitor_score. This is the full when/when-not/alternative pattern.

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