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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the bar is lower, yet the description adds substantial context: the data source (Central Bank official monthly table), the exact computation, the graceful-degradation behavior when data is missing, and the Jalali date convention.

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 sentences, front-loaded with the operation and legal basis, then the formula and fallback rule. Dense but every element earns its place; only the mixing of Persian/English legal terms adds minor parsing overhead.

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 no output schema, the description does need to convey return behavior: it says a number is returned when the table is loaded and a limitation message plus link otherwise. It stops short of specifying the result's unit or precision, a minor gap for a six-parameter calculator.

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%, so baseline is 3, but the description adds meaning the schema does not: it ties the month parameters to the formula (index of payment month ÷ index of due month) and explains why start_month matters (ruling 850 reads that month's index). The Jalali note reinforces the schema's date semantics.

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 (calculate) and resource (late-payment damages / خسارت تأخیر تأدیه), names the governing legal basis (art. 522 ق.آ.د.م, ruling 850), and gives the exact formula used. This clearly separates it from the sibling calculators (diyeh, mahrieh, arbitration fee, etc.).

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 tells the agent what to do when the CBI table is unavailable (return the limitation plus the official link, never approximate), which is genuine invocation guidance. It does not, however, explicitly state when to prefer this tool over sibling calculators or what conditions make it inapplicable.

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