Cash Flow

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds a genuinely useful behavioral fact — totals come from YNAB's own monthly aggregates rather than recomputed transactions — but says nothing about return shape, currency units, or how months are bucketed when sinceDate and months overlap.

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?

Three short sentences, front-loaded with the core purpose, then a provenance note, then the alt-tool routing hint. Nothing is 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?

With no output schema, the description should hint at the shape of the result (a monthly series of income/spending totals). It conveys the concept of monthly aggregates but not the structure, and it does not explain how optional planId/budgetId aliasing affects the call in practice.

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 months, planId, budgetId, and sinceDate are already documented, including the default of 6 months and the sinceDate-overrides-months precedence. The description adds nothing beyond that; baseline 3 applies.

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 resource and comparison (income versus spending, month by month) with the derived outcome (surplus). It also differentiates from the sibling ynab_balance_forecast, which covers projection, so an agent can route correctly 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 names the alternative (ynab_balance_forecast) and the condition that selects it (projected balance). It does not exclude adjacent siblings like ynab_spending_by_category or ynab_plan_summary, which also surface spending totals, so exclusions are incomplete.

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