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

Annotations only declare destructiveHint=true, so the description carries most of the load and does it well: it discloses the implicit 'Sample Client' side effect and a concrete failure mode (403 on free-plan limits). It stops short of saying whether the change is reversible or what permissions are required.

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 compact sentences, front-loaded with the core action and the highest-risk caveat. The trailing 'Paymo: POST /api/projects.' is endpoint detail of marginal use to an agent but costs little.

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 create tool with 8 parameters and no output schema, the description covers side effects and one error case but omits the return value (e.g., the new project id needed for follow-up calls) and any permission requirements. Adequate but with a real gap for a creation workflow.

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 baseline is 3, but the description adds meaning the schema lacks for client_id — the auto-created 'Sample Client' fallback when it is omitted. The other seven parameters gain nothing beyond their schema descriptions.

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 and resource ('Create a project') that is immediately distinguishable from siblings like paymo_create_task and paymo_create_time_entry. It does not explicitly contrast itself with alternatives, but the resource is unambiguous.

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?

Gives useful conditional context — omitting client_id triggers auto-creation of a 'Sample Client', and free plans hit an active-projects limit (403). However, it never states when to prefer this tool over paymo_list_projects/paymo_get_project or what prerequisites (e.g., valid client_id, user ids) are needed.

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