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

Annotations cover the safety profile (readOnly/idempotent/non-destructive), and the description layers on the things they cannot express: newest-first ordering with undated last, no offset pagination, 1-50 limit, count semantics, count 0 on no match, and two specific isError triggers (non-calendar updated_since, unknown category). 'Free, no auth' removes any auth guesswork.

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?

Every sentence carries a distinct behavioral fact — scoping, filter logic, ordering, pagination, error cases — with the most decisive claim ('the only library lookup') front-loaded. No filler or restatement of the title.

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 an output schema present, return values need not be described, yet the description still clarifies count and empty-result behavior. For a 7-parameter, zero-required search tool with annotations already covering safety, nothing needed to invoke it correctly 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 coverage is 100%, so the baseline is 3, but the description adds filter-combination semantics ('category, tag, type, featured, and updated_since are AND filters') and an error contract for unknown category that the schema does not state. It also restates some schema content (substring fields, limit range), so it is additive rather than fully value-adding.

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?

Opens with a specific verb+resource ('Find third-party library source cards') and immediately scopes it against the whole toolset: 'This is the only library lookup: text, exact filters, and newest-first browsing.' An agent can distinguish it from get_source and list_changes 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?

Gives explicit routing: use get_source for a single known id, use list_changes for unpaged cross-catalog sync, and omit query to browse newest sources. The conditions that select each alternative are stated, not implied.

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