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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=false, so safety is covered structurally. The description adds real value on top: it discloses that only "live" guides are returned and that paid body/depth content is never exposed, which is the kind of scope limit annotations cannot express. It does not clarify error behavior for invalid slugs.

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 sentences, front-loaded with the payload description, then the scope limit, then the slug inventory. Every element earns its place. Minor deduction for the trailing ellipsis, which leaves the slug list visibly truncated without saying how to retrieve the rest.

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?

An output schema exists, so return fields need not be re-explained, and annotations cover the safety profile. The description supplies the remaining essentials — which resource, which inputs, what is excluded. Only gap is the incomplete slug enumeration (23 known, 8 listed) and no guidance on unknown-slug failure.

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 single slug parameter is already documented — baseline 3. The description earns an extra point by enumerating the 23 known slugs (eight shown), which is materially richer than the schema's four generic examples and lets the agent validate input without guessing.

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?

Specific verb + resource ("returns one live guide's") plus an enumeration of the exact fields returned (title, subtitle, access, book count, reading time). It also draws a hard scope boundary — "card-level metadata only, never the paid body/depth content" — so an agent immediately knows this is not a content-fetch tool. No sibling shares this resource, and the named guide slugs make the target 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 gives clear context for use: fetch lightweight card metadata for a known guide, and it implicitly excludes the deep paid content case. What it lacks is an explicit routing statement (e.g., which tool to call for the full guide body) or a note on handling unknown slugs. Clear context, no named alternative, so a 4.

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