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

The annotations already declare this to be a read-only, idempotent, closed-world tool, and the description adds genuinely useful context that they do not cover: the data is a Tehran free-market rate, it is denominated in Toman (IRT) rather than an ISO quote currency, and it includes change against yesterday. Permissions and rate-limit behavior remain unstated.

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 content is front-loaded: the English sentence states the scope and the returned fields first, and the Persian sentence mirrors it. The bilingual duplication doubles the length, but it is a deliberate localization rather than 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?

There is no output schema, so the description usefully lists the return values: buy, sell, mid, change against yesterday and the data timestamp. Combined with the single well-documented parameter, this is close to complete for a small lookup tool, with only pagination or failure behavior unspecified.

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 the only parameter is documented with the pattern, examples and an ISO 4217 explanation. The description adds nothing about the code parameter itself, so the schema does the heavy lifting and the baseline score of 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: today's Tehran free-market rate of one currency, quoted in Toman, with the buy, sell and mid fields and the change against yesterday. 'Today's' implicitly separates it from get_history and get_rates_table, but it never names those siblings, so an agent must still infer the boundary.

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 word 'today's' implies that this tool covers only the current snapshot, which hints that get_history should be used for past data, but there are no explicit when-to-use or when-not-to-use instructions and no mention of convert or list_currencies as alternatives. Usage is only implied.

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