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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, and the description adds valuable context beyond them: the exact temporal selection rule ('the row picked is the latest valid_from at or before that date'), the no-role behavior, and the cost ('Free'). There is no contradiction with the annotations.

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 two short sentences that front-load the core purpose ('Show the hourly rate...') and append only necessary selection and edge-case details. 'Free.' earns its place by flagging cost without adding noise.

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 simple read-only lookup with zero required parameters, the description covers purpose, selection logic, the optional-role branch, and cost; remaining defaults are already present in the schema. The safety profile is carried by annotations, so nothing needed to invoke the tool correctly is missing.

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 coverage is 100%, so the schema already documents each parameter's format and defaults. The description adds meaning by tying date to the valid_from snapshot lookup and by clarifying that omitting role triggers a full-card listing, which goes beyond the baseline.

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 opening clause uses a specific verb ('Show') with a clear resource ('hourly rate') and qualifiers (role, date, currency), so an agent knows exactly what the tool returns. It also distinguishes itself from siblings like rate_set by describing a read-only lookup and the no-role mode that lists every card.

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 a clear conditional usage: when no role is given, it lists every card; with a role, it returns the rate for that role as of a date. It does not explicitly name rate_set as the write/update alternative, so the when-not guidance is implicit rather than explicit.

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