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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and an output schema exists, so the remaining burden is light. The description adds that output includes a prior-period comparison and that the data is meant for reasoning rather than presentation, but says nothing about precision, rounding, or coverage gaps that an analyst would care about.

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 short sentences, zero filler, with the core capability and the sibling routing stated up front. Nothing redundant with the title or annotations.

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 annotations covering safety and an output schema defining the return shape, the description only needed to convey scope and the sibling split, which it does. Period semantics and the summary flag are fully documented in the schema, so no agent-relevant information 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%, including a full enum for period and a detailed explanation of the summary flag, so the schema carries parameter meaning. The description adds no parameter-specific syntax or defaults, which is the expected baseline when the schema is complete.

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 the resource precisely — categorized spending plus a prior-period comparison — so the agent knows what comes back without opening the schema. It also names and distinguishes itself from the sibling spending_breakdown (analysis vs display), though it never uses an explicit verb for the retrieval action.

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?

'Numbers to reason with — to display, use spending_breakdown' gives an explicit alternative and the condition that selects it. It stops short of stating exclusions or prerequisites (e.g., when prior-period comparison is unavailable for period=all), so it is clear but not exhaustive.

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