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

Annotations already declare readOnlyHint=true and openWorldHint=false, but the description adds crucial behavioral traits: it explicitly states the tool never returns guide body/depth text (free or gated) and instructs to never summarize/excerpt content not returned. It also lists known slugs, providing context about valid inputs. These go beyond annotations to clarify limitations.

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 description is concise, front-loaded with the primary function, and each sentence adds value: what it returns, what it doesn't return, how to handle the output, and known slugs. No filler or redundancy.

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 simple single-parameter metadata tool with an output schema, the description covers return fields, limitations (no body text), the recommended follow-up action (canonicalUrl), and valid slug examples. It is complete for an agent to correctly invoke and interpret 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 schema describes the slug with examples, but the description adds a list of known slugs (19) and clarifies the slug must correspond to a live guide. This enriches the parameter meaning beyond the schema's basic description, even though schema coverage is 100%.

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 clearly states the tool returns metadata for a single live guide (title, subtitle, access, book count, reading time) and explicitly differentiates it from siblings by focusing on guides and card-level metadata. It also distinguishes from other content types like library work or magazine pieces, making the purpose unambiguous.

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 implies usage (when you need guide metadata) and provides guidance on how to handle the result (send reader to canonicalUrl, never summarize). However, it does not explicitly compare with sibling tools or state when to prefer this over search_library or other retrieval tools. The usage guidance is present but not exhaustive on alternatives.

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