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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds useful behavioral context by specifying the output format ('as markdown') and the scope ('one full ... page'). It does not mention error handling for invalid slugs, but with annotations present this is a minor gap.

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?

Two tightly written sentences. The first states the core action, resource, and output format; the second gives routing guidance and concrete examples. No wasted words or repetition of the schema.

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 one-parameter tool with full enum documentation, strong annotations, clear sibling routing, and an explicit statement of the markdown return format, no meaningful context is missing. The description is sufficient for an agent to select and invoke the tool 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%: the schema describes 'slug' as 'Which page to fetch' and enumerates all valid values. The description mentions 'by slug' but adds no additional semantics beyond what the schema already provides. Baseline 3 is appropriate.

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 names a specific verb ('Fetch'), a specific resource ('one full Yappy documentation page as markdown'), and the key mechanism ('by slug'). It also implicitly differentiates itself from search_documentation by emphasizing 'full page' and 'markdown' versus an excerpt.

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?

The description explicitly states when to use this tool: 'after search_documentation when an excerpt is not enough and you need the whole page.' It even gives concrete examples, making the decision boundary clear relative to its siblings.

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