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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so safety is covered. The description adds real behavioral context beyond that: it flags that outputs include a break-even year, that unverified coverage comparability is surfaced rather than assumed, and that 'no carrier prices are invented' — i.e., it computes only from user-supplied quotes and never fabricates market data. That last point is the kind of trust signal annotations cannot express.

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 sentences: purpose, inputs, outputs plus caveats. Front-loaded with the comparison framing, and no sentence is redundant — the final clause about not inventing carrier prices could easily have been omitted but earns its place as a trust qualifier.

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?

An output schema exists, so return values need not be spelled out in detail, yet the description still names the headline outputs. With 11 parameters and only 6 required, the description's mention of entering premiums and upgrades tells the agent what to gather; annotations cover the safety profile. Nothing material is missing for correct invocation.

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 the per-field semantics (annualize a six-month premium, whole US dollars, upgrade costs) are already fully documented. The description groups the inputs conceptually into net premiums, underlying-limit upgrades, and switching cost, which helps orient the agent but adds no format or edge-case detail beyond the schema. 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?

Specific verb-plus-resource: 'Compare the total cost of keeping existing home and auto insurance with standalone umbrella coverage versus moving all three to a bundle.' It names both sides of the comparison and the deliverable (first-year/multi-year totals, savings, break-even year), which distinguishes it from umbrella_calculator and umbrella_limit_planner siblings that compute a single figure rather than a cross-scenario delta.

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?

The scenario is clearly framed — user already has home and auto, is deciding whether to add standalone umbrella or rebundle all three — and it lists what inputs to supply. It gives no explicit exclusions or named alternatives (e.g., when to prefer umbrella_limit_planner for sizing), so the agent must infer routing from the comparison framing rather than being told outright.

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