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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description earns credit for the economics rather than repeating them: "Free to call and changes nothing" clarifies that this call itself consumes no quota, which is the non-obvious fact an agent needs before calling it speculatively. The billing sentence ("A check uses one word per word checked for each tool run") is slightly convoluted and could momentarily be misread as this tool costing words, but the follow-up sentence disambiguates.

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?

Front-loaded with the trigger condition, then return contents, then cost. Three sentences, no filler. The billing sentence is the weakest link — its phrasing is denser than it needs to be — but nothing is extraneous.

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?

With no output schema and no parameters, the description carries the full burden of telling the agent what comes back, and it does so field by field including the reset date and plan link. Combined with annotations covering safety and no arguments to document, an agent has everything needed to call this correctly and interpret the result.

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?

The tool takes zero parameters, so the baseline is 4; there is nothing for the description to compensate for. The schema is empty with additionalProperties=false, consistent with the description's no-argument framing.

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?

Starts with a concrete trigger ("when the user asks how many words they have left") and a concrete resource (word balance), then enumerates exactly what comes back: plan name, used/left this month, monthly limit, bonus words, reset date, plan link. The sibling tools (check_plagiarism, detect_ai, get_scan_result) are all content-analysis operations, so an agent can tell this is the account-quota lookup without opening any 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?

Gives two explicit use conditions: a direct user question about remaining words, and a pre-flight check before submitting a long text to see if the balance covers it. That second case is a genuinely useful proactive trigger an agent wouldn't infer. No explicit when-not or alternative is named, but with no param-less sibling covering the same ground, little is left ambiguous.

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