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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds substantive context: the 365-day cap without a key, the extended archive with a Pro FX key back to 1360/1981, and the 400-point ceiling that causes longer windows to be sampled. These are non-obvious behavioral traits an agent could not infer from schema or annotations.

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?

Information is front-loaded: what is returned, then how to scope it, then limits and access tiers. Every sentence carries content, though the closing Persian sentence largely duplicates the opening and is the one element that does not earn extra space.

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 some work here by indicating each point carries both Gregorian and Jalali dates, and by warning that long windows are sampled rather than returned in full. What it never shows is the actual response shape (field names, series structure), leaving a small gap for a data-returning tool.

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 the baseline is 3, but the description adds meaning beyond the schema: Jalali dates such as 1404-01-01 are accepted in the date params, and the sampling rule clarifies what `from`/`to` actually returns for long windows. It does not restate the ISO 4217 pattern or the `days` bounds, which the schema already covers.

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+resource: 'Daily Tehran open-market closing rate of a currency in Toman' with Gregorian and Jalali dates. It clearly distinguishes a historical series from a point-in-time read, though it never names the sibling get_rate to make the contrast explicit.

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 tells the agent how to choose between `days` and `from`/`to`, and explains the key-based access tiers (anonymous = last 365 days, Pro key = full archive). It gives no explicit exclusions against siblings like get_rate or get_rates_table, so it stays below a 5.

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