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

readOnlyHint=true already establishes this as a safe read, so the description is not the sole carrier of the safety profile. It adds no further behavioral context, however: nothing about whether periods may overlap, must be equal length, or whether the result is a delta, ratio, or raw side-by-side totals. With annotations covering safety, a 3 is the right level.

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?

A single sentence with no filler, and the core purpose is front-loaded. It is efficient, though borderline terse for a tool with four required date parameters.

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 comparison tool with no output schema, the description states the metric (spending) but not the shape of the comparison (delta vs. percentage vs. per-category breakdown) or constraints relating period 1 to period 2. Adequate to call it, but not complete.

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% — all four date parameters are documented with format and role in the schema. The description adds nothing beyond this (no ordering rules, no equal-length requirement), so the 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?

The description names a specific verb (compare) and resource (spending) with a clear scope: two time periods. It distinguishes itself implicitly from list-style siblings like get_expenses or get_spending_summary, but never explicitly contrasts with them.

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?

There is no guidance on when to choose this over get_spending_trends or get_spending_summary, nor any stated prerequisites or exclusions. The agent must infer that this is the two-period delta tool from the name and description alone.

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