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

Annotations are minimal (all hints false), so the description carries the full burden of behavioral disclosure. It discloses the visibility timeout mechanism, redelivery behavior, cost structure (charged first delivery only), free redeliveries, zero charge when nothing is due, authentication methods, and the equivalent HTTP route. This goes far beyond what annotations provide.

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 moderately long but every sentence earns its place; it covers purpose, behavior, cost, authentication, and routing without redundancy. The first sentence states the core function clearly, and subsequent sentences add necessary operational detail. It is well-structured and front-loaded with the most important information.

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 tool with no output schema, the description fully covers the call's behavior: what happens on success (delivered envelope), what happens on empty queue (explicit message and no charge), cost implications, authentication requirements, parameter purposes, and the relationship to ack/nack. Given the tool's complexity (polling, timeout, redelivery, billing), this is a complete and self-contained description.

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 schema already documents all three parameters with 100% coverage, so the baseline is 3. The description adds meaningful context: it explains when to use agent_key (if headers cannot be set), elaborates on visibility_timeout semantics (claimed item returns if not acked), and clarifies the mailbox concept. This provides real value beyond the schema.

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: "Collect the next due task envelope from your mailbox." It clearly specifies the action (poll for the next due task), the resource (mailbox/envelope), and the key constraint (one envelope per call). This distinguishes it from siblings like inbox_ack and inbox_nack, which handle acknowledgment, and work_take/claim, which are alternative work-retrieval mechanisms.

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 implies usage context: you poll to claim an envelope, then ack it when done, with a visibility timeout that returns it to the queue if not acked. It also states when nothing is due ("We say so and charge nothing"). However, it does not explicitly contrast with alternative tools like work_take or claim, nor does it say 'use this instead of X'. The guidance is clear but not exhaustive.

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