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

With no annotations, the description carries the full behavioral burden. It usefully discloses the pay-per-call cost model ($0.005 per call, USDC on Base), which is real value an agent cannot get from structured fields, but it says nothing about latency, failure modes, or how the paid call is settled. The cost disclosure lifts it above a bare 2.

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?

A single compact sentence with the purpose front-loaded and the enumerated metrics immediately after. The pricing parenthetical is short and materially relevant, so nothing is wasted.

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, and the description compensates by naming the returned metrics (chars, words, lines, ZWNJ count) plus the cost of a call. Only the 'options' parameter behavior (e.g. the digits setting) is left entirely to the schema, a minor 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%, so both parameters (text, options) are already documented in the schema, and the description adds no syntax or format detail beyond naming ZWNJ as a computed metric. Baseline 3 is appropriate when the schema does the heavy lifting.

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?

Names a specific operation ('statistics') on a specific resource ('Persian text') and enumerates exactly what is measured (chars, words, lines, ZWNJ count). The metric list implicitly separates it from extraction-style siblings like fa_sentences or fa_keywords, though no sibling is named explicitly.

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?

There is no statement of when to reach for this tool versus the many other fa_* tools, and no prerequisites or exclusions. The only contextual note is pricing, which is a cost fact rather than usage guidance.

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