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

Annotations already cover the safety profile (readOnlyHint, destructiveHint=false, idempotentHint), so the bar is lower. The description still adds real behavioral context beyond them: no activity side effects, candidate sources (Educaplay bank + stock library), and the divergent return behavior of a single-query vs multi-query call.

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?

It is dense but front-loaded: the non-mutating distinction and the sibling routing come first, then batching rules, then the downstream tool. Every sentence carries information, though the clause chain is long enough that a shorter phrasing was possible.

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-value burden and does so: it describes candidate shape ('source' and a descriptive 'title'), the differing result size for single vs multi queries, and where the returned ids go (set_item_images). Nothing an agent needs to call or chain this tool 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 baseline would be 3, but the description adds meaning the schema lacks: 'one query per concept, up to 10' clarifies the intent of the array, and it explains that page is only relevant for a single-query call, which the schema does not state.

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 states a specific verb+resource ('List image candidates') and immediately scopes it ('WITHOUT adding anything to the activity'), which cleanly separates it from the mutating sibling illustrate_items. An agent can pick the right tool 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?

It gives explicit when-to-use ('only when the user asks to see or to choose among options') with quoted trigger phrases, and names the alternative (illustrate_items) plus the condition that selects it ('to put images on the activity'). Both branches are unambiguous.

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