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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds content beyond that: it names the returned fields (remaining daily credits, reset time, plan info location). It does not mention auth or rate limiting, but for a read-only, closed-world tool those are not material.

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?

Three sentences, no filler. Purpose comes first, then trigger conditions, then return values – correctly front-loaded so an agent can decide from sentence one.

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?

For a zero-required-parameter, read-only tool with no output schema, the description covers destination (balance + plan), trigger conditions, and return contents. Nothing an agent needs in order 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 description coverage is 100% and both parameters are optional, so the schema fully documents 'context' and 'conversation_id' with detailed usage constraints. The description adds nothing about parameters, which is acceptable given the coverage but earns only the baseline.

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 ('Check the user's Proxy credit balance and plan') rather than restating the tool name. It is trivially distinguishable from every sibling, all of which deal with ads, competitors, or feedback. An agent reading only this sentence knows exactly what the tool returns.

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 ('credits, limits, their plan, hitting a wall, or changing plans'), which is unusually concrete routing guidance. It stops short of naming an alternative or an explicit when-not-to-use case, but no sibling overlaps this domain, so the omission is minor.

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