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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false; the description reinforces this with "Changes nothing" and adds a business precondition (rental must be in progress) that annotations cannot express. It does not explain openWorldHint behavior, failure modes, or what happens with a stale management_id.

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?

Everything present is useful, but the core purpose ("prices the extra days") is buried mid-way through a long run-on sentence whose conditional clauses are hard to parse. The example earns its place; the structure could be front-loaded with the verb first.

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?

An output schema exists, so return values need no explanation. Combined with the sequencing rule, the in-progress precondition, identifier-selection guidance, and a concrete call example, an agent has what it needs to invoke this correctly; the only omission is the optional market parameter.

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?

With only 50% schema description coverage, the description compensates well: it explains where management_id comes from and the conditional rules for choosing management_id plus reservation_number versus reservation_number alone. It demonstrates the ISO-8601 offset format for new_return_at via the example, but never mentions the market parameter, leaving one of four params undocumented in both places.

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 action ("prices the extra days") and resource (a rental extension), and "Changes nothing" signals it is a read-only quote rather than the actual mutation. It stops short of explicitly contrasting with the sibling request_extension, which is the tool an agent could most easily confuse it with.

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 an explicit trigger ("user wants to return the car later"), a sequencing prerequisite ("after verify_reservation_management"), and conditional routing for the two identifier paths depending on whether the code went to the user's e-mail or the account is connected. The precondition "Only a rental in progress can be extended" tells the agent when not to call it.

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