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

Goes well beyond the annotations (readOnly, non-destructive, not idempotent) by disclosing a non-obvious behavior: existence is not checked, so a key naming nothing still yields a URL that answers 404. It also describes the return shape per key (a URL, or the reason it got none), which matters since there is no output schema.

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 tight sentences, each doing distinct work: what it is, how to supply keys, and what comes back plus the 404 caveat. Batch positioning is front-loaded, and nothing is repeated from 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?

With no output schema, the description carries the return-shape burden and does so adequately (per-key URL or failure reason), and it flags the missing existence check. Only minor gaps remain, such as what the 'reason it got none' cases look like.

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 would be 3, but the description adds real semantics: keys must be full keys as reported by list/find tools, and 'each distinct key gets its own entry' clarifies that results are keyed and deduplicated. Expiry and bucket semantics are left entirely to the schema.

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 specific verb+resource ('pre-signed download URLs for several objects in one bucket') and immediately positions it against the sibling: 'the batch form of create_download_link'. An agent can distinguish this from create_download_link without opening either 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?

Tells the agent where keys come from ('as list_objects or find_objects reported it') and that this is the batch variant when several objects are needed. It stops short of an explicit 'use the single form when only one key' statement, but the batch framing makes the routing clear.

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