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

With no annotations, the description carries the full burden and does so well. It discloses the rate-change history (3% → 5% → 8% → 10%), the reduced rate's start date of 2019-10-01, the back-dating rule for invoices and credit notes, and that history mode returns changes with statutes. These are meaningful behavioral traits beyond what annotations would likely convey.

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 dense sentences with no filler. The core function is front-loaded, and the second and third sentences provide behavioral context that an agent actually needs rather than repeating schema content. 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?

For a 5-parameter tool with no annotations and no output schema, the description covers the key behaviors: date-specific rates, reduced-rate eligibility, optional tax computation, and history mode. Minor gaps remain around the exact output shape when `amount` is passed and what happens if both `date` and `as_of` are provided, but these are not critical for basic 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 baseline is 3 because the schema already documents all five parameters in detail. The description adds useful semantic context for `date` (back-dating matters more than expected) and `history` (returns changes with statute), raising it above baseline. It does not add much for `as_of` or `amount`, which are already well covered by the schema.

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 first sentence clearly identifies the resource as the Japanese consumption tax rate in force on a date, including national/local split and the reduced 8% rate. This distinguishes it from the payroll and insurance sibling tools. It lacks an explicit verb like 'returns', but the functional intent is unmistakable.

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 gives concrete usage context: back-dated invoices and credit notes against old sales should use the original transaction date, and it warns that date matters more often than people expect. It does not name alternatives or explicitly state when not to use the tool, so it falls short of perfect routing guidance.

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