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

Goes well beyond the readOnly/idempotent annotations by disclosing that the call does not consume a check and is not billed, how key types (pc_live_, tw_, hex x-tw-bundle-client, anon:) select different caps, and the returned fields. This is richer behavioral context than structured fields provide.

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-loads the purpose in one sentence, then layers usage, exclusions, and return values. Dense but each sentence carries information; the tier explanation is slightly sprawling but earns its place as non-obvious behavioral detail.

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, the description compensates by naming the return fields (subject_kind, limit, used, remaining, resets_at) and covering the zero-argument anonymous case. Nothing needed to call it correctly is missing.

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 already 100%, so the baseline is 3, but the description adds real semantics: a pc_live_ key reads that key's own cap and a tw_ key does not select this cap. It reinforces rather than merely repeats the schema's exclusions.

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 ('Read how many free PayCheck merchant checks this caller has left today') with clear scope. It explicitly distinguishes itself from the similarly-named get_quota and the Toolweather quota, so an agent can route without opening the 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 explicit trigger conditions ('before a run of check_merchant calls, or after an HTTP 402') and explicit exclusions (not SpendGate's cap, not the health-check quota, not key minting). Alternatives are named with their exact sibling tool names.

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