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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and openWorld, so the safety profile is covered. The description adds something the annotations do not: 'No token needed, just the @divindi.io address', which tells the agent no authentication step is required before calling. It stops short of saying what the response contains (raw amount, formatting, thresholds for 'low'), which keeps it from a 5.

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?

Three short clauses, each doing work: what it checks, when to call it, and the fallback when the balance is low. The scoping and prerequisite information is front-loaded with no 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 single-parameter read tool with full annotation coverage and no output schema, the description covers purpose, prerequisites and the follow-up path. The only gap is the shape of the result and what counts as 'low', which would help an agent decide whether to chain into request_topup.

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% and there is only one parameter, so the schema already explains the email field. The description reinforces the format constraint ('just the @divindi.io address') but adds no new meaning such as whether other domains are rejected. Baseline 3 applies.

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 names a specific verb and resource — checking how much USDC a DiviMail address holds — and ties it to a concrete purpose (sending email or paying). An agent can distinguish it from siblings like divimail_pay or divimail_request_topup without opening any 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?

It gives an explicit trigger ('Call before divimail_send or divimail_pay if unsure') and a named alternative for the low-balance case ('use divimail_request_topup'). Both the when-to-use and the routing decision are stated, not implied.

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