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

With no annotations and no output schema, the description carries the full disclosure burden and does so well: it details what each returned figure represents and even notes the average income is observed from transaction history and separate from subscription-based expected income. It says nothing about permissions, currency-conversion behavior, or performance, which caps it below 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?

The purpose is front-loaded in the opening clause, and each subsequent item earns its place by specifying a return metric. It is a heavy run-on enumeration, though, and could be tightened with a list rather than one long sentence.

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?

With no output schema, the description must explain return values, and it does so comprehensively, plus it adds the six-month income calculation context. The only real gap is that the type filter from the schema is never acknowledged, creating a small mismatch with the 'all active subscriptions' framing.

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% and the single enum parameter is fully documented in the schema, so the baseline is 3. The description never mentions the type filter and instead says 'all active subscriptions', which could mislead an agent into thinking the tool cannot be scoped to bills or installments.

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 states a specific aggregate operation ('Aggregate summary across all active subscriptions... split by direction') and enumerates exactly which metrics it produces (monthly cost, yearly cost, expected income, active counts, average income, share spent). This scope is clearly distinct from the listing tools get_subscriptions / get_subscription_by_id, so an agent can route correctly.

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?

It supplies concrete trigger questions ('how much am I spending on subscriptions per month?', 'how much recurring income do I have?', 'what share of my income goes to subscriptions?') that map cleanly to invocation intent. It does not, however, name alternative tools or state when NOT to use it (e.g. use get_subscriptions for the raw list), so it stops short of explicit alternative routing.

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