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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds the endpoint mapping and the shape of returned fields, which is modestly useful, but says nothing about truncation behavior, auth requirements, or rate limits beyond what the schema already notes.

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 sentences, front-loaded with the resource and its fields. The trailing endpoint reference earns a little place as an API mapping hint, though it is close to filler for an agent that only needs to call the tool.

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 list tool with full parameter documentation, this is largely complete: the field list compensates for the absent output schema and the annotations cover safety. Only the lack of any usage/filtering guidance keeps it short of full marks.

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%, so all four parameters (limit, where, active, include) are already thoroughly documented in the schema, including the no-pagination truncation caveat. The description adds no parameter meaning beyond that, which is the expected 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?

States a specific verb (List) plus resource (clients) and even enumerates the returned fields (id, name, contact details, active flag) and the backing endpoint. It is unambiguous against siblings like paymo_list_projects or paymo_list_users, though it never explicitly differentiates itself from them.

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?

No when-to-use guidance is given. There is no mention of when to reach for this versus a filtered client lookup, no prerequisites, and no indication of when the 'where' escape hatch should be preferred over the typed filters.

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