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

With no annotations present, the description carries the full burden and does disclose real behavior: Persian+English stopword filtering, frequency ranking, and a cost signal ('$0.01 per call, USDC on Base') that an agent must know before invoking. It does not cover failure modes or the 100k-character limit, which lives only in the schema.

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?

Four short sentences, front-loaded with the core action, then usage, then return, then pricing. No filler or repetition.

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 no annotations, so the description must carry return and edge-case detail. 'Returns the ranked keywords' is the bare minimum – it doesn't say whether results are strings or keyword/count objects, nor what the default limit is. Adequate but with clear gaps for a text-processing 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 67%, below the high-coverage baseline, and the description adds no parameter-level meaning at all. 'limit' is entirely undocumented and 'options' only has a terse example in the schema, so the description fails to compensate for the gap; the frequency-ranking mention only loosely implies a limit.

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 gives a specific verb+resource ('Extract the frequent keywords from Persian text') plus the ranking mechanism, so an agent can distinguish it from fa_stats, fa_sentences, or fa_normalize. It never names a sibling explicitly, which is the only thing separating it from a 5.

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 states concrete use cases ('build a search index, an automatic tag list, or a topic summary for a Persian document'), giving clear context for when the tool is appropriate. It offers no exclusions or named alternatives, so it stops short of the 5 bar.

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