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

With no annotations, the description carries the full burden and does well: it discloses the cost model (€0.004 per request, 6000 chars), the auth requirement (Bearer API key in Authorization), and the invariant behavior (facts and Markdown preserved). It does not say what happens past the 6000-char limit or on invalid tone values, leaving a modest gap.

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 core behavior, then cost/auth, then a compact parameter list — front-loaded and dense with no filler sentences. The trailing 'Parameters — ...' enumeration is slightly list-like but each clause adds information.

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?

Given five undocumented schema parameters, no annotations, and an output schema that covers returns, the description supplies the behavior, pricing, auth, and parameter meanings an agent needs. The remaining hole is required-ness/defaults semantics, since zero required params with null defaults is unusual and unexplained.

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 0%, so the description must compensate, and it largely does: each of the five parameters gets meaning, including tone examples ('friendly, formal, marketing'), the length value set and its default ('same (default) | shorter | longer'), and the role of instructions as extra rules. It doesn't explain that all parameters are optional/nullable or what happens when text is omitted.

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 ('Rewrite in a given tone and length') plus the invariant it preserves ('keep facts and Markdown'), which tells an agent exactly what transforming operation this performs. It doesn't explicitly distinguish itself from near-siblings like summarize, translate, or readability_score, which keeps 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?

Usage is implied by the described inputs ('optional language switch', tone, length), so an agent can infer the scenario, but there is no explicit 'use this when / use translate instead' routing. The presence of translate, summarize, and readability_score as siblings makes that omission material.

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