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

Annotations only declare destructiveHint=true, so the bar is low, and the description adds real side-effect disclosure beyond them: omitting client_id silently auto-creates a 'Sample Client', and free plans hit an active-project limit returning 403. It omits permission/role requirements and what is returned, keeping it from a 5.

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?

Three short sentences, front-loaded with the action and followed by the highest-value caveats; nothing is buried. The trailing 'Paymo: POST /api/projects' restates an endpoint an agent cannot act on, which is minor filler.

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 single-required-param create with fully documented schema and no output schema, the description covers the critical hidden behavior (implicit client creation) and a failure mode (403 on plan limits). It lacks permission prerequisites and any indication of what the created project returns (e.g., an id for follow-up calls).

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?

With 100% schema coverage the baseline is 3, and the description goes beyond the schema by explaining the omission semantics of client_id (auto-creation of a Sample Client), which the schema's terse 'Client the project is for' does not convey. Other params are left entirely to the schema.

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+resource ('Create a project') that cleanly distinguishes it from read siblings like paymo_get_project and paymo_list_projects and from paymo_create_task. It does not explicitly name an alternative or contrast scope, so it stops short of a 5.

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?

There is no guidance on when to use this versus alternatives (e.g., when to create vs reuse an existing project, or when to call paymo_list_projects first). The notes address edge-case behavior (auto-created Sample Client, free-plan 403) rather than usage selection, so the agent must infer context.

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