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

No annotations are provided, so the description carries full burden. It states that the reply is 'plain-text' and sent to the 'authenticated sender', which implies authorization context. However, it does not disclose side effects (e.g., does it mark the message as replied? Is the reply visible elsewhere?), potential rate limits, or whether the operation is destructive. It is clear but not comprehensive.

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 a single, compact sentence that front-loads the action and key constraints. Every word serves a purpose, and there is no redundancy. It could be slightly more concise by removing 'included' (the inclusion is implied), but overall it is well above average.

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 5 parameters (60% schema coverage), no output schema, and no annotations. The description is functional but lean. It explains the core action but omits important contextual details like return value (is there a confirmation ID?), error scenarios (e.g., invalid inbox_id), or idempotency behavior beyond the schema hint. For a tool with moderate complexity, it meets a minimum viable level but leaves gaps.

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 60%, with fields like `text`, `token`, `inbox_id`, and `idempotency_key` having descriptions in the schema. The description adds little beyond, only mentioning 'plain-text' for the reply content. For `message_id`, the description does not help clarify what this refers to, and the schema lacks a description for it. The overall added value from the description is marginal.

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 uses a specific verb ('Send') and identifies the resource ('plain-text reply' directed at the 'authenticated sender of an inbound message'). This clearly distinguishes it from sibling tools like create_inbox or list_messages, as it is the only tool focused on sending a reply to a message sender.

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 implicitly states when to use the tool (when you need to reply to an inbound message), but it provides no explicit guidance on when not to use it, nor does it mention alternatives. Sibling tool names like get_message or list_messages hint at possible related actions, but no direct comparison or exclusion is given.

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