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

readOnlyHint=true already tells the agent this is a safe, non-mutating read, so the description does not need to re-establish safety. It adds modest value by specifying the endpoint and clarifying that both current and available balances are returned, but says nothing about auth requirements, rate limits, or whether 'available' excludes pending holds.

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 that are front-loaded with the core action, with the endpoint reference and the optional time qualifier trailing. No padding or redundancy.

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 simple two-parameter read tool with full schema coverage and a readOnlyHint annotation, the definition covers what the tool does and the one optional modifier. No output schema exists, but explaining return fields is arguably already done by naming current and available balance.

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?

Schema description coverage is 100%, so both account_id and at_time are already documented in the schema, including the ISO 8601 format and the 'as of that moment' semantics. The description's 'optionally as of a point in time' merely restates the at_time parameter, adding no new meaning.

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 and resource ('Retrieve an account's current and available balance') and names the exact fields returned, so it is clearly distinguishable from sibling reads like get_account or get_transaction. It does not, however, explicitly contrast itself with those siblings.

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?

There is no when-to-use or when-not-to-use guidance and no alternatives named among the many sibling get/list tools. The only contextual note is that the balance can be read 'as of a point in time', which is parameter information rather than usage guidance.

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