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

The annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered structurally. The description still earns credit for naming the concrete business consequences that are absent (no credit consumption, no purchase, no subscription change, no checkout initiation), which is exactly the kind of domain-specific assurance annotations cannot express.

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?

Two short sentences, the core purpose first and the negative scoping second. Every clause either states what is returned or rules out a plausible but wrong expectation, so nothing is padding.

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-argument read tool with rich annotations and an output schema describing the return shape, the description supplies everything an agent needs: what is read, whose balance it is, and what side effects will not occur.

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 no parameters, so there is nothing for the description to disambiguate; the baseline for a zero-parameter schema applies, and the prose introduces no confusing pseudo-inputs.

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 opening sentence gives a specific verb ('Reads') and resource ('the current account's available Fotor credit balance'), so it is immediately distinguishable from every sibling, which are task submission and URL/model lookups rather than balance queries.

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?

The second sentence clearly frames this as a read-only balance lookup and rules out consuming, purchasing, changing a subscription, or initiating checkout, which tells the agent when not to reach for it. It stops short of naming which sibling to use for those excluded actions, so there is no explicit alternative routing.

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