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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, not open-world), so the bar is lower; the description still adds real context: free, no sign-up, no cookies or tracking, the widget fills its container width, and it follows the reader's light/dark mode. What it does not cover is the exact shape of the returned HTML or any sizing/attribute caveats, which is the only remaining gap.

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 value proposition (one iframe line, free, no sign-up, no tracking) and the routing rules are front-loaded, and the closing exclusion sentence is well placed. The 21-item calculator enumeration is bulky, but it is partly justified because it annotates bare enum keys with display names.

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 an output schema present, return-value explanation is not required, and the description covers purpose, trigger, exclusion, embed properties, and the calculator catalogue. Currency behavior is left entirely to the schema, and no guidance is given on placement or sizing caveats beyond width-filling, leaving a small completeness gap.

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% and both parameters have enums, so the schema carries the syntax burden (baseline 3). The description adds value by mapping every cryptic enum key to a human-readable calculator name (e.g. rule_of_72 → 'Rule of 72 calculator'), which helps the agent pick the right one; the currency parameter itself is not elaborated in the description.

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 deliverable ('The HTML to put one of SmartFin's free calculators on a website') and immediately differentiates from the sibling smartfin_calculate_* tools by declaring it is not for computing anything. An agent can route correctly 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?

It gives an explicit positive trigger ('Use when the user wants a calculator on their own site or asks how to add one') and an explicit exclusion with the alternative ('Do not use to calculate anything (use the other smartfin_ tools)'). Both when-to-use and when-not-to-use are covered.

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