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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is covered. The description's enumeration of returned fields adds real value given there is no output schema, but it says nothing about error behavior, permissions, or pagination/format.

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 compact clauses, front-loaded with the resource and its scope. The trailing endpoint path is somewhat redundant with the tool name but still useful for API mapping, so the definition is efficiently sized.

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 two-parameter read with full schema coverage and safety annotations, the description supplies the missing piece — an indication of what fields come back, since no output schema exists. The field list is a partial sketch rather than a full contract, but nothing critical for correct invocation is absent.

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 both parameters are documented in the schema with their provenance (business_id from keypay_list_businesses, pay_run_id from keypay_list_pay_runs). The description adds no parameter-level meaning beyond the raw endpoint path, so the baseline of 3 applies.

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 gives a specific verb+resource ('One pay run by id') and enumerates the returned fields (pay schedule, period, date paid, finalised status, notation), which distinguishes it from siblings like keypay_get_pay_run_summary, keypay_get_pay_run_totals, and keypay_get_pay_run_payslips. It stops short of naming an alternative, so it is clear but not fully self-differentiating.

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?

Usage is implied (fetch a single pay run when you have its id), and the schema clarifies the id comes from keypay_list_pay_runs. There is no explicit statement of when to prefer this over the summary/totals/payslips siblings, so guidance is only implicit.

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