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

Beyond annotations, the description discloses API key requirements, credit costs for sending versus verifying OTP, the prohibition on bulk use, and the return shape (JSON delivery receipt or verification token). These details materially help an agent understand side effects and constraints.

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 front-loaded with the core action and stays dense with relevant details. It is slightly long due to parenthetical examples and cost details but every sentence carries useful 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 six-parameter tool with no output schema, the description covers purpose, action modes, cost model, API key requirement, restrictions, and return values. An agent has enough context to invoke it correctly without needing more explanation.

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 description adds meaningful semantic context by linking action=verify_otp to zero credits and other actions to 25 credits, which helps an agent choose the right action mode.

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: send transactional email or verify OTP. It explicitly distinguishes 1-to-1 transactional use from bulk marketing blasts, so an agent can identify the correct tool and avoid sibling tools like send_push_notification.

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?

It gives clear usage context: transactional 1-to-1 emails and managed OTP verification, with an explicit prohibition on bulk marketing. It does not name alternative sibling tools for related operations, so it falls short of a 5.

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