Summarize invoices or vouchers (totals, not rows)

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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description reinforces rather than contradicts that ('Read-only'). It adds a genuinely useful non-obvious trait: the response stays small regardless of ledger size, and rows are never returned — the key behavioral difference from the list tools. It does not mention the fetch-cap trade-off or what happens when maxItems truncates the aggregation, which the schema alone implies.

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 dense sentences: the core behavior (aggregate, no rows, which sums) is front-loaded, followed by routing guidance and the size guarantee. No filler, and every clause carries information an agent needs to choose the tool.

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 7-parameter read tool with no output schema, the description still explains what the response contains (counts, net/tax/gross sums, grouped buckets), which is the information an output schema would otherwise provide. Combined with 100% schema coverage and safety annotations, nothing an agent needs to call it correctly is missing.

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 every parameter including enums and defaults is already documented, and the description mostly restates the grouping options. It adds the framing that grouping can be by 'nothing' for a single total, but no date-format, cap, or side semantics beyond the schema — baseline 3 is appropriate.

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 (aggregate), specific resources (invoices or vouchers), and the defining constraint (counts plus net/tax/gross sums, never rows). It also names the enumeration of grouping dimensions, so an agent can distinguish it from every list_* sibling without opening the schema.

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?

Explicitly says to use this for totals instead of the list tools, and supplies concrete example intents ('revenue in Q2', 'expenses by supplier'). The alternative (sevdesk_list_invoices / sevdesk_list_vouchers) is named implicitly by category and the selection condition is stated outright.

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