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

Annotations already carry readOnly/idempotent/non-destructive/closed-world, and the description adds real value beyond them: determinism, no stored state, and concrete execution limits (time, result size). Minor flaw: it states a 64 KB input cap while the schema allows maxLength 262144, which could cause an agent to truncate valid input.

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?

Purpose is correctly front-loaded in the first sentence. However, the entire body is duplicated verbatim in Spanish and English, so roughly half the tokens repeat already-stated content, and the generic "When" sentence is the least informative part of that duplication.

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?

An output schema exists, so return values need no explanation; the description covers purpose, exclusion, determinism, and execution limits for a 4-parameter tool. The one real gap is the size-limit conflict with the schema, which leaves the true input ceiling ambiguous.

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; the description earns an extra point by explaining the tie-break ordering (frequency, then first appearance) and the intent of case folding and whitespace exclusion, which the terse schema entries do not. The `top` parameter is left to the schema.

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 and resource ("Counts how often each grapheme appears") plus output ordering and the two optional modifiers. It also names the sibling it is not (word-frequency), so an agent can discriminate it without opening a schema.

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 has an explicit "When" clause and an explicit "Not for" clause that names the alternative (word-frequency). The "when" wording is abstract ("transform, compare or measure exactly instead of approximated") rather than naming concrete triggers like 'compute character histogram', so it stops short of a 5.

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