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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds genuinely new context: the auth requirement ('Requires: token') and the behavioral fact that order_vps draws on this balance automatically when sufficient, which helps an agent interpret the number.

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 short sentences, front-loaded with the core action and each carrying distinct information (return values, cross-tool behavior, auth requirement). No filler or repetition.

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 does describe what comes back (credit balance plus currency) and states the token requirement, which is enough for a zero-parameter read tool. It stops just short of details like balance units or whether the value includes pending charges.

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 parameter-wise to clarify, and the description instead spends its words on the return payload (balance and currency), which 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?

The description states a specific verb and resource ('Return the account's prepaid credit balance and currency'), so an agent immediately knows this is a read of account credit. It does not explicitly name the sibling it contrasts with (topup_balance), relying on the resource name to do the differentiating.

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 only implied: the note that `order_vps` spends from the balance tells the agent why the balance matters, but there is no explicit 'use this when... / not when...' guidance or pointer to topup_balance for adding funds. Context exists but selection criteria must be inferred.

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