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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered. The description adds one genuinely useful behavioral fact — the composite key means no single-record retrieval exists — but says nothing about pagination cost or result volume beyond what the schema states.

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?

Two short sentences, front-loaded with the resource definition and followed by the constraint. No filler, though the parenthetical '(composite key)' could have been folded more smoothly into the second clause.

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 read-only listing tool with 100% schema coverage and no output schema, the description covers what the entity is and the key structural limitation. Only the shape of the returned mapping rows is unaddressed, a minor gap since the schema and annotations carry the rest.

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 100%, so all four parameters (page, per_page, site_id, contract_id) are already documented in the schema. The description adds no format, default, or combination guidance, so this sits at the baseline for fully-covered schemas.

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 (List) and the exact resource (contract-to-site mappings), then defines the semantics of that resource — which contracts cover which sites. This separates it cleanly from create_contract_site/delete_contract_site without needing the reader to infer the join-table nature of the entity.

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?

The note 'No single-record lookup (composite key)' implicitly tells the agent it must list-and-filter rather than fetch by ID, which is useful routing information. However it never states when to prefer this over list_contracts or list_sites, nor what the contract_id/site_id filters are for.

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