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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description usefully reinforces the cost profile with 'Costs no credits.' It also discloses that the listed costs are 'live' (dynamic), which annotations don't convey. It stops short of describing refresh timing or caching behavior, so it's strong but not exhaustive.

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 tight sentences: purpose first, then the enumerated cost keys, then the usage imperative. The parenthetical list is dense but each key maps to a real output field, so it earns its space rather than 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?

An output schema exists, so return-value documentation is unnecessary, and the description already covers what the tool does, when to call it, and that it is free. For a simple zero-argument read tool, nothing an agent needs 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?

Zero parameters, so there is nothing for the description to compensate for; the baseline for a no-arg tool is 4. The description adds no parameter information because none is needed.

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+resource (returns the signed-in user's credit balance plus live per-action costs) and even enumerates the cost keys returned. This is clearly distinct from every sibling, which are spend/create/delete operations.

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 an explicit when-to-use rule: 'Call it before any tool that spends credits and tell the user the price.' It also implies the when-not (nothing to check for read-only siblings) and mandates the downstream action of surfacing price to the user.

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