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

Annotations already declare readOnlyHint and idempotentHint, so the safety profile is covered. The description adds useful non-obvious behavior: the valid_from selection rule ('latest valid_from at or before that date') and the output nuance about naming any later booked row. This goes beyond the annotations and schema.

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 brief and front-loads the core purpose and selection rule in one dense sentence. 'Free.' is a small extra that adds marginal value but does not significantly clutter the description.

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 no output schema, the description helpfully explains what the answer contains: the picked row and any later already-booked row. Combined with readOnly annotations and full schema parameter coverage, this is sufficient for a single-SKU read tool, though exact output format is not specified.

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% and all four parameters already have clear descriptions. The tool description provides only a high-level summary ('one currency and tier') rather than per-parameter elaboration, which is acceptable given the schema carries the full meaning.

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 uses a specific verb and resource: 'Show the price of one SKU as of a date, in one currency and tier.' The singular SKU/date scope clearly differentiates it from siblings like sku_list, price_list_text, and rate_get, which cover broader or different queries.

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 singular scope implies when to use it, but the description never explicitly names alternatives or states when not to use it. An agent must infer the choice between this and price_list_text or sku_list from context rather than from direct guidance.

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