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

Annotations already indicate a write, non-idempotent operation; the description adds the concrete business rule that the free plan allows only one client and the error contains upgrade_url. This failure-mode detail is useful, though the description does not discuss other side effects or post-conditions.

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 sentences, each with unique information: when to trigger, a caution against speculative use, and the free-plan limit/error behavior. No fluff; the actionable trigger is placed first.

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 moderate-complexity creation tool with no output schema, the description covers when/user intent, explicit non-usage, and the key plan-boundary error. It does not explain success response or required permissions, but these are not required for an agent to invoke it correctly.

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 only 40%, and the description compensates by tying 'rate' and 'billing email' to create triggers. However, it does not add meaning to two other non-schema-covered fields (name is implied, address is unmentioned) and does not fully compensate for the low coverage.

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 specifies the action (create), the resource (client), and the exact confirmation conditions. It clearly distinguishes from the sibling workspace.create_project by focusing on client creation and non-existent-client confirmation.

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?

It explicitly says when to use (user names a non-existent client and confirms, or asks to add with rate/billing email) and when not to use (do not create speculatively while logging time). It does not name alternative sibling tools, but the client-creation context leaves no direct alternative, so the guidance is strong.

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