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

Annotations already disclose that this is a non-read-only, non-destructive, non-idempotent, closed-world operation. The description adds the contact lookup prerequisite but does not explain duplicate-logging risk, reversibility, or what happens after logging, so it adds only moderate behavioral context beyond annotations.

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 tight sentences with no wasted wording. The primary action is front-loaded, and the prerequisite follows immediately.

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?

The tool is a mutation with annotations covering safety and idempotency, and the schema fully documents inputs. The description covers purpose and the key contactId prerequisite; only minor gaps remain around duplicate handling and post-call behavior, with no output schema to explain return values.

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 five parameters are already documented in the schema. The description adds a useful relationship between a mentioned client and contactId, but does not explain the other parameters beyond what the schema already provides.

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 names a specific verb and resource: 'Log billable hours for a client or project.' It is clear what the tool does, though it does not explicitly distinguish itself from any sibling, likely because no sibling is a close alternative.

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 gives a concrete prerequisite: call lookup_contact first if a client is mentioned to obtain the contactId. That is useful routing guidance, but it does not discuss when not to use the tool or compare it against alternatives.

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