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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds genuinely non-obvious behavior beyond that: the date parameter defaults to the last day of the current fiscal period, which changes what the call returns when date is omitted. No mention of error or auth behavior, hence not a 5.

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?

One front-loaded sentence carrying the resource, the default behavior, and the endpoint path. No filler.

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?

There is no output schema, so the description must carry the return semantics; it identifies the value as an end-of-day balance but says nothing about the shape (scalar vs. amount/currency object). For a simple read-only lookup with fully documented params, this is nearly sufficient.

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 coverage is 100%, so the two parameters are already documented (id sourced from cashctrl_list_accounts, date format yyyy-mm-dd). The description adds the default value for date, which the schema does not state, giving real incremental 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: the balance of one account at the end of a day, plus the underlying endpoint GET /account/balance. It is clearly distinguishable in substance from cashctrl_get_account, but never names or contrasts with that sibling explicitly, so it stops short of a 5.

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?

Usage is only implied: the agent can infer this is the tool for 'what was this account's balance on date X'. There is no statement of when to prefer it over cashctrl_get_account or cashctrl_get_report_data, and no prerequisites mentioned.

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