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

Beyond the readOnlyHint annotation, the description discloses detailed computation rules: residents use progressive rates up to 24% after reliefs, non-resident employees pay the higher of 15% or resident-rate, and other non-residents pay 24%. It also explicitly states that the calculator branches on residency status, adding substantial behavioral context that annotations alone do not provide.

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?

The description is exactly three sentences, with no wasteful content. It front-loads the core scope, then efficiently provides the key behavioral rules, and closes with a value-add note about correct branching. Every sentence earns its place.

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?

Given the tool's complexity (residency-dependent rates), the description covers the essential calculation rules for all status categories, and the schema covers parameter details. Even without an output schema, the purpose as a calculator makes the return value obvious. The description and structured data together provide a complete picture for an agent to select and invoke the tool correctly.

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?

The schema already covers all three parameters with 100% description coverage, so the baseline is 3. The description adds value by clarifying the nonResidentOther status—specifically mentioning that non-resident directors and most other non-resident income are taxed at 24%—and by explaining how reliefs fit into the resident calculation, adding meaning beyond the schema's parameter descriptions.

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 clearly states the tool's specific purpose: 'YA 2026 Singapore tax for residents, non-resident employees, and non-resident directors — including personal reliefs.' This establishes a unique scope (Singapore YA 2026) and distinguishes it from sibling tools like income_tax_hong_kong or generic income_tax. The verb 'calculates' is implied and the resource is precisely defined.

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 description provides clear context for when to use the tool: for Singapore income tax calculations with varying residency statuses. It notes that the calculator 'runs the correct branch instead of silently assuming everyone is resident,' implying it's the right choice for non-resident scenarios. However, it doesn't explicitly name alternative tools or state when not to use it, so it falls just short of a 5.

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