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

Annotations already declare readOnlyHint true and destructiveHint false, so the description correctly aligns. The description adds behavioral context by detailing the specific output fields (available balance, current balance, etc.) and environment compatibility, which is valuable beyond annotations.

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?

The description is three sentences with no wasted words. It front-loads the core purpose, lists outputs, and provides usage guidance—all concise and structured effectively.

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?

Given the tool has no parameters, an output schema is present (inferred), and the description covers all needed aspects: purpose, output details, and integration hints. The description is fully sufficient for an agent to correctly invoke and interpret results.

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?

There are zero parameters, so the input schema is fully covered. According to guidelines, baseline for 0 params is 4. The description does not need to add parameter-level details.

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 specifies a clear verb ('List') and resource ('all Mercury bank accounts and balances'), and explicitly states what is returned (account IDs, names, balances, currency). It also distinguishes itself from related sibling tools by explaining how to use the account IDs with mercury.transactions and mercury.send.

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 description clearly states when to use this tool (to list accounts and balances) and works in both sandbox and production. It provides follow-up actions (use account IDs with other tools), but does not explicitly state when not to use or list alternative tools, which is acceptable given the tool's simplicity.

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