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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, non-destructive), so the bar is lower. The description nonetheless adds real behavioral context: standard APYs are sourced, promos are shown separately, and minimum balances and monthly fees are factored in, plus an 'estimates, not advice' disclaimer. It doesn't discuss result ordering or per-account detail, keeping it short of a 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?

Two tight sentences with the computational scope front-loaded and the methodology and disclaimer trailing. Every clause carries information, though the parenthetical '(promos shown separately)' and disclaimer make it slightly denser than strictly necessary.

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 an output schema present, return values need not be described, and annotations carry the safety profile. The description supplies methodology and a disclaimer, leaving only minor gaps such as how many accounts are returned and any ordering, which the output schema presumably covers.

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% with explicit ranges (1-120 months, 0-10M balance), so the schema already documents semantics fully. The description mentions the N-month horizon and a balance but adds no format or interpretation beyond the schema, matching the baseline 3.

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 verb ('Project interest') and resource ('a balance over N months'), plus the scope ('at every high-yield savings account VaultRubric tracks'). This clearly separates it from siblings like estimate_fees and compare_platforms without the agent opening any 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?

Usage is implied by the description's scope (projecting savings interest across tracked accounts), but there is no explicit when-to-use, when-not-to-use, or named alternative vs estimate_fees or compare_platforms. The 'Estimates, not advice' caveat hints at positioning but doesn't route the agent.

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