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

Annotations already declare readOnlyHint=false, idempotentHint=true and destructiveHint=false, so the mutation safety profile is covered. The description adds real semantic behavior beyond that: the operation grants eligibility rather than assignment, and the eligibility is scoped to unscheduled units. It does not mention failure modes (e.g. the brand mismatch) or side effects on existing crew, so it stops short of 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, each earning its place: the positive definition, the disambiguating negation, and the routing rule. The core effect is front-loaded before the exclusions.

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 3-parameter tool with no nested objects and full schema coverage, the description supplies the semantic model needed to call it correctly and to route away from schedule_job. It does not describe the return or confirmation behavior and there is no output schema, which is a minor remaining gap.

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%, and the schema already explains that brand is optional and refused if it differs, and that project_id/resource_id come from find_project and find_resource with a 'never guess' warning. The description adds nothing further about parameters, so the baseline 3 applies.

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 ('Add an engineer to a project's crew') and immediately defines the effect ('lets them claim any of its unscheduled units'). It also explicitly distinguishes the operation from sibling schedule_job, so an agent can tell them apart without opening either schema.

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 an explicit when-not clause ('This is NOT the same as booking them onto one'), names the alternative tool and the trigger for it ('If the user named a particular day or unit, use schedule_job on that unit instead'), and supplies a fallback for ambiguity ('When you cannot tell which they meant, ask'). This is about as complete as routing guidance gets.

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