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

With no annotations provided, the description carries the full behavioral burden and does so thoroughly. It discloses the async confirmation-link flow, the pending-not-sent semantic, the reply routing to reply_to_email, the email_undeliverable failure mode including causes, and the instruction not to retry the same address. This goes far beyond the structured schema.

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 longer than average but every sentence carries critical operational information. The core action is front-loaded, then the decisive caveat about pending confirmation, followed by failure handling and status tracking. It is well organized and avoids filler.

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 side-effectful tool with no output schema and no annotations, the description covers the essential lifecycle: message creation, confirmation delivery, user action required, reply routing, failure conditions, and follow-up via status_key. Nothing an agent needs to invoke it correctly and communicate results to the user 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?

Schema coverage is 100%, so the baseline is 3. The description adds meaningful value beyond the schema, especially for reply_to_email: it receives the confirmation link and the poster's reply, and the user must be asked for it rather than guessed. post_id is also contextualized as coming from search_listings or get_listing.

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 first sentence states a specific verb ('send'), a resource ('message to the poster of an active Capmus listing'), and clearly distinguishes this from the read/search/list sibling tools. The intent is unambiguous even without opening the schema.

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 clear operational guidance: tell the user to check their inbox, report the message as pending, and handle undeliverable confirmation emails by requesting a new address. It does not explicitly state when not to use the tool or name check_message_status as the alternative, but it references the status_key flow, providing clear context.

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