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

Annotations provide no behavioral hints (all false), so the description carries the burden. It discloses the key behavior: the same role/currency/date replaces that row rather than adding one, which is critical for an agent to understand persistence semantics. It also notes 'Free,' which may imply no cost. This is substantive transparency beyond the 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?

Two sentences, front-loaded with the core action and fields. Every clause earns its place: the replacement rule and the 'Free' note are both relevant. No fluff or repetition.

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 mutation tool with 6 parameters, 83% schema coverage, and no output schema, the description covers the essential behavioral semantics (replacement, field units, default currency implicitly). It doesn't mention edge cases like validation or side effects, but those are minor for a setter. The sibling list reinforces its role. Adequate 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 83%, so the schema already documents most parameters. The description reinforces hourly_minor as whole minor units and alludes to the start day, but adds little beyond what the schema provides. It does not introduce new semantic insight beyond the schema's own 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 states a clear verb ('Set'), a specific resource ('hourly charge-out rate on a labour card'), and enumerates the key fields (role, currency, hourly_minor, start day). It also clarifies the replacement semantics, distinguishing it from a simple add. This differentiates it from siblings like rate_get and sku_set without ambiguity.

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 makes the tool's purpose obvious (setting a rate) and implies it is the counterpart to rate_get for retrieval. It does not explicitly state exclusions or when to prefer an alternative, but the context is clear enough for an agent to select it appropriately. No misleading guidance.

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