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

Annotations already declare non-destructive, idempotent, closed-world, so the bar is lower, and the description adds genuinely new behavior: the assignment grants visibility over the customer and all its projects, and privilege hierarchy limits who can be targeted. It does not say what happens on duplicate assignment or how to undo the grant (remove_user_from_customer exists), leaving reversal implicit.

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 tight sentences, front-loaded with the effect, then prerequisites, then the prohibition on passing an organization id. No filler or restatement of the title.

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 mutation with annotations and full schema coverage, this covers the important unknowns: what the grant confers, where the ids come from, and the privilege ceiling. Remaining gaps are duplicate-assignment behavior and how to revoke, both inferable from the sibling set.

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 org_user_id is the OrganizationUser id, not the Firebase id. The description adds a secondary discovery path (get_employee_timesheet) and the rule that no organization parameter is accepted, which is a modest increment over the schema rather than new semantics for customer_id or idempotency_key.

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 (assign an organization member to a billing customer) and adds the concrete consequence — the user gains visibility of that customer and all its projects. That effect clause distinguishes it from the project-level assignment sibling without naming it, though no explicit contrast with assign_user_to_project is made.

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 real preconditions: both ids are required, org_user_id can be discovered via get_project_team or get_employee_timesheet, and the organization id must never be passed because context fixes it. It also states a targeting constraint (cannot assign a user more privileged than yourself). It stops short of saying when to prefer assign_user_to_project or remove_user_from_customer instead.

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