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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds real value by clarifying that the balance is customer-scoped and shared across all of the customer's keys, and that ledger entries are bundled into the response.

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?

A single sentence with the scoping caveat in parentheses, front-loading the primary return value and appending the secondary one. No wasted words.

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 reasonably covers what comes back (balance plus latest ledger entries). It is complete enough for a no-argument read tool, though it does not say how many ledger entries 'latest' means or in what unit credits are expressed.

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 there is nothing for the description to compensate for. Baseline 4 applies; schema coverage is 100% and no parameter meaning 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?

Names the specific resource (remaining contract credits) and the scope (this API key's customer, shared across keys) plus secondary content (latest ledger entries). An agent can distinguish it from the write-oriented sibling buy_credits, though the differencing is implicit rather than stated.

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?

No when-to-use guidance, no mention of alternatives such as buy_credits, and no prerequisites. The read intent is only inferable from the wording 'remaining' and the annotations, not stated.

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