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

The description says each renewal adds a 15-minute lease and the total is capped at 6 hours, which implies repeated calls change state. The annotations declare idempotentHint=true, so a repeated identical call should produce the same result. This is an annotation contradiction.

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 sentences, no filler, with the core behavior front-loaded and the use case stated compactly. The 15-minute increment and 6-hour cap are concrete and immediately useful.

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?

The description covers the main behavior, duration, cap, and motivation, but leaves the optional 'as' parameter unexplained and does not address what happens at the cap. Combined with the idempotency contradiction, the agent lacks full operational clarity.

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?

The input schema provides zero description coverage, so the description must explain parameters. It names message_id and lease_id, but does not describe their roles, formats, or the meaning of the optional 'as' parameter. This is only partial compensation for the schema gap.

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 opens with a specific verb and resource: 'extend the lease on a message.' It clearly explains that the tool renews a lease for a message being worked on, and names the two required identifiers. This is immediately distinguishable from siblings like bus_cancel or bus_nack.

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 description gives concrete usage context: use it to keep working instead of letting the lease expire and the message be re-offered to someone else. It does not name or contrast sibling tools explicitly, but the intended scenario is clear enough for an agent to route to this tool.

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