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

Annotations already declare readOnlyHint=true and destructiveHint=false, lowering the bar. The description adds real behavioral context beyond that: the period-vs-point-in-time semantics of from/to, the per-ledger aggregation, and the auth requirement ('Needs the user's Cotlet API key with access to this app'). It stops short of mentioning pagination or response shape.

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?

Front-loads the core purpose and then layers constraints; nearly every sentence carries information. It is slightly verbose (the 'not a list of every booking' aside and the API-key note could be tightened) but no sentence is wasted.

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 read-only, three-optional-parameter tool with annotations covering the safety profile, the description supplies the semantics, aggregation behavior, and auth needs an agent requires. Since there is no output schema, the 'Returns one balance per ledger' note usefully covers the return, though it could say more about format.

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 baseline is 3, but the description goes further by explaining how from and to interact (period balance vs. balance on a date) and what cost_center_id filters on ('narrow it'). That adds interpretive value the terse schema descriptions do not fully convey.

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 every ledger') and immediately scopes it ('one balance per ledger'). It explicitly distinguishes itself from the mutation-listing sibling ('This is a balance per ledger, not a list of every booking'), so an agent can tell it apart from list_mutations/list_ledgers without opening schemas.

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?

Explains the conditions that shape the result: 'With from set, the balance covers only that period; with to set, it is the balance on that date, inclusive. Add a cost center ID to narrow it.' It implies when to use it versus a bookings listing, but does not name a specific alternative tool, so it falls short of a full when/when-not/alternatives statement.

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