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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so safety is covered. The description adds real behavioral detail beyond them: results are aligned on the same fields and returned in the caller's input order, which matters for reliable comparison output.

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?

A single sentence with zero filler; the count constraint, the id source, the ordering rule, and the purpose are all packed in without redundancy.

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?

For a one-parameter read tool with no output schema, the description is nearly sufficient: it conveys input source, cardinality, ordering, and that results are field-aligned. It does not tell the agent which fields are compared or what happens with an invalid/duplicate id, but those are minor.

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 must carry the param semantics — and it does: it identifies plan_ids as ids sourced from search_plans, states the 2–10 range (matching minItems/maxItems), and specifies that array order is preserved in the output.

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 ('put side by side') and resource ('plans'), with explicit bounds (2 to 10) and an ordering guarantee. It is clearly distinct from get_plan (single plan) and search_plans implicitly, though it never names the single-plan alternative 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?

'ids from search_plans' names the upstream tool that supplies inputs, and 'to help a traveller choose' gives the decision-making context for using it. It stops short of stating when NOT to use it (e.g., for a single plan, use get_plan).

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