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

Annotations already declare readOnly/not-destructive. The description adds meaningful context beyond them: billing model ($0.003/call, first 25 free, failed calls free) and an explanation of why repeats are charged, which plausibly explains the idempotentHint=false. It restates "reads or computes only and changes nothing," which overlaps with annotations, but the pricing detail is genuine added value.

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 and usage are front-loaded in the first two sentences, and the trailing pricing sentence is information-dense. The mid-paragraph example slightly interrupts flow and the character count is at the upper end, but every sentence carries content.

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?

No output schema exists, and the description names the computed metrics well enough that an agent knows what comes back, and it fully covers billing/auth via /credits and x402. Minor gaps remain on output shape (per-metric fields) and the boundary of 'English text' support.

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?

With one required parameter at 100% schema description coverage, the schema already defines the argument and the description's example (text=The quick brown fox...) shows usage form. No additional format constraints (max length, encoding, language limitations beyond English) are provided, so baseline 3 is appropriate.

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 specific verbs and resources: counts characters/words/sentences/paragraphs, estimates reading and speaking time, computes Flesch reading-ease and grade level. This enumerates the exact outputs and clearly separates it from siblings like text_diff or text_extract.

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?

"Use to check the length and readability of a draft" gives clear usage context. However, no alternatives or when-not-to-use conditions are named, and no prerequisites beyond payment are noted.

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