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

Annotations already convey idempotency and non-destructiveness, but the description adds critical behavioral context: lease expiration and reclaimability, the run_id ownership rule (foreign run cannot steal a live lease), and the strict error handling for unknown keys. It also implies state change (leasing) consistent with readOnlyHint=false. No contradiction with annotations.

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?

The description is three sentences, each densely packed with distinct information: the core function, the re-claim workflow, and the error behavior. It is front-loaded with the primary purpose and uses precise, structured phrasing without fluff. Every clause earns its place.

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 tool has no output schema, so the description must convey what the agent gets back. It states it 'leases ... messages for processing,' which implies the response contains the leased messages, but it never explicitly describes the return shape (e.g., list of messages, lease metadata). Given the complexity and the importance of knowing what to expect, this is a minor gap. Otherwise, the description covers the full workflow, error handling, and parameter ranges.

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 the baseline is 3. The schema already documents each parameter in detail (limits, defaults, ranges, idempotency, lease expiry). The description largely repeats this information rather than adding new parameter-level meaning. While it integrates the parameters into the workflow, it doesn't go beyond what the schema already explains.

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 precise verb and resource: 'Lease up to limit oldest-first pending inbox messages for processing.' It clearly distinguishes this from the sibling tools (mailbox_ack, mailbox_check, mailbox_send, register) by framing it as the claim/lease operation, and even names mailbox_ack as the follow-up step. This is a specific, unambiguous statement of what the tool does.

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 explicitly sequences usage: 'Ack them with mailbox_ack, THEN claim again for the rest.' It also explains the idempotent re-claim behavior and cautions about foreign runs and lease expiry. This provides both when-to-use and how-to-proceed guidance, leaving no ambiguity about the intended workflow.

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