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

Annotations already declare readOnlyHint=true, destructiveHint=false and a closed (openWorldHint=false) corpus, so the safety profile is covered. The description adds two genuine facts beyond that — the scope is a 'bounded public library' and missing evidence is reported rather than erroring — but nothing about volume or ranking behavior.

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?

Three dense sentences with the core purpose front-loaded and the two usage modes immediately after. Every clause carries information, though the locator sentence is packed tightly enough to need a second read.

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, and the description covers purpose, the two invocation modes and the missing-evidence case. For a 4-parameter, 0%-coverage schema the undocumented 'question' and 'limit' parameters are the one remaining gap.

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 0%, so the description carries the full burden, and it supplies the non-obvious cross-parameter rule that a locator must be paired with exactly one source ID, plus the semantic effect of multiple source_ids. It leaves 'question' and 'limit' (default 5, max 5) entirely unexplained.

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?

States a concrete verb+resource pair ('Return passages, edition, locator and provenance') and names the corpus it draws from ('bounded public library'). It is distinguishable from search_library and inspect_source in spirit, but never names or contrasts a sibling explicitly.

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 real conditional guidance: one source ID plus a full locator retrieves an exact indexed locator, while multiple IDs switch the tool into edition-comparison mode. It stops short of stating when-not-to-use-this or naming search_library as the alternative for open-ended discovery.

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