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

Annotations already indicate readOnly and idempotent, and the description adds valuable behavioral detail: the full status lifecycle, terminal:true meaning stop waiting, and reply_declined:true meaning the recipient closed without answering. This goes well beyond what structured annotations provide and helps an agent decide whether to keep polling.

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 compact, front-loaded with the status list, and uses two sentences to define the crucial terminal and reply_declined flags. Every phrase earns its place with no redundancy.

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 single-parameter read-only status tool with an output schema and safety annotations, the description covers the needed context: what statuses to expect, what the reply field is, and what terminal:true means for stopping. No critical information for correct invocation is missing.

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 only provides message_id as a required string, so the description carries the semantic burden. The phrase 'message you sent' clarifies that the ID must refer to a message the caller originated, which is useful context beyond the raw parameter name. It could be more explicit about where the message_id comes from (e.g., bus_send), but it is still reasonably clear.

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 verb and resource: checking the status of a message you sent. It enumerates the exact status values (queued, leased, delivered, replied, dead_letter, expired, cancelled) and mentions the reply once it exists, making the tool's scope clear and distinct from sibling send/reply/ack/cancel tools.

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 phrase 'a message you sent' gives clear context: this tool is for checking messages you originated rather than received ones. It does not explicitly name alternatives like bus_inbox or bus_history, but the sent-message framing provides enough guidance for a competent agent.

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