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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds that output is composed email text with a subject line and that tone defaults to polite — useful, but it never states explicitly that nothing is sent, nor does it disclose how stage selection interacts with missing dates.

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?

Two compact sentences with no filler: the stage logic comes first, the tone default second. Every clause conveys information an agent would otherwise have to guess.

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?

With 10 parameters, no output schema, and several optional fields (late_fee, pay_link, business_name, invoice_number), the description leaves the agent to infer what each optional field does to the generated email and what form the return value takes. It is adequate for the core call but thin for a tool with this many optional inputs.

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 70%, so the schema carries most of the load. The description contributes real meaning for two parameters: tone ('polite by default; firm on request') and the implicit role of today vs. due_date in determining the reminder stage. It says nothing about late_fee, pay_link, business_name, or invoice_number beyond what the schema already documents.

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?

States a specific verb and resource ('Writes the right payment reminder') and enumerates the four invoice stages it handles, plus the inclusion of a subject line. An agent can tell this generates reminder copy rather than computing dates or fees, so the sibling calculators are effectively differentiated even though none is named.

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?

Usage is implied rather than stated: the stage is chosen from where the invoice sits ('before due, due today, late, or a final notice'), which suggests feeding in the current date, and 'polite by default; firm on request' hints at the tone parameter. There is no explicit when-to-use vs. when-not-to-use or reference to the sibling tools that supply due-date and late-fee data.

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