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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds a genuine behavioral detail beyond that: ids are scoped to the current business and an out-of-scope id raises an error rather than returning empty/404 semantics. It still says nothing about response shape, pagination, or side effects (none expected).

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 short sentences, zero filler, with the core identity ('one pay run by id') front-loaded and the constraint trailing. Nothing repeats the title or annotations.

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 one-param read tool with annotations covering safety, the description covers what is needed; the 'same fields as list_payruns' note usefully compensates for the absent output schema. It does not say what happens for a malformed id, but that is a minor gap.

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 0% for the single required 'id' param, so the description must carry the load. It clarifies that id identifies a pay run belonging to this business, which adds scoping meaning beyond 'type: string', but gives no format hint (e.g. numeric vs opaque string).

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?

Clear verb+resource ('One pay run by id') and it explicitly relates itself to the sibling 'list_payruns' by stating it returns the same fields. An agent can tell it fetches a single pay run rather than enumerating them, though it does not spell out the single-vs-list choice as a routing rule.

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 one pay run when you already hold its id. There is no explicit 'use this instead of list_payruns when...' guidance, but the error note about non-owned ids gives the agent a usable precondition.

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