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

Annotations already declare readOnlyHint=true, idempotentHint=true and openWorldHint=false, so the safety profile is covered. The description adds that it returns spend and recent calls, which is useful return-shape context, but says nothing about auth requirements, rate limits, or how 'recent' is bounded.

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?

One well-formed sentence with the action and returned fields front-loaded, no filler. Slightly redundant with the title's phrasing but not wasteful.

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?

A simple one-parameter read tool with full schema coverage and no output schema; the description tells the agent what comes back (balance, spend, recent calls), which is the main missing piece. Adequate for the tool's low complexity.

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 description coverage is 100% for the single 'key' parameter, so the schema already documents format (yatc_...). The description merely restates that same format, adding no new semantics; 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?

Specific verb 'Returns' paired with clearly named resources (remaining balance, spend, recent calls) and the key type (yatc_...). It is distinguishable from credits_quote by naming the data it returns, though it never explicitly contrasts the two.

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 resource named — an agent would infer this is for inspecting an existing key's state rather than obtaining pricing. However, there is no explicit when-to-use statement and the sibling credits_quote is never mentioned, leaving the routing choice to inference.

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