Projects Create User Assignment

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

Annotations already declare write, non-idempotent, open-world, non-destructive, so the description is not required to establish the safety profile. It adds genuine behavioral context the annotations lack: a pre-request validation failure when the matching allocation value is absent, and that allocation_mode is forwarded verbatim despite an API naming inconsistency between `fixed` and `fixed_hours`.

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?

Front-loaded with resource, route and date format, which is good, but the percent/allocation_mode rules largely restate what the schema's own property descriptions already say, so several sentences are duplicated rather than additive. The wording around the fixed-mode naming discrepancy is also dense enough to take two readings.

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 an 11-parameter write tool at 18% schema coverage, the description explains the allocation-mode machinery well and an output schema handles return values. It still leaves a third of the parameters (bill_rate_id, status_option_id, user_id, description) with no semantics anywhere, which is a meaningful gap for correct invocation.

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?

With only 18% schema description coverage, the description carries most of the burden and does so for the hard parts: assignable_id semantics, the percent (0–1 fraction), hours_per_day and fixed modes, the date format, and the mode-to-value mapping. It leaves the meanings of bill_rate_id, status_option_id, description and user_id entirely undocumented in both places.

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 a user to a project, phase or leave type') plus the concrete route POST /users/{user_id}/assignments, so the operation is unambiguous. It does not explicitly contrast itself with near-identical siblings such as projects_create_assignment or projects_create_project_assignment, leaving the agent to infer that this one is user-scoped.

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?

The description explains the internal mode rules (which value each allocation_mode requires) and that a missing value causes refusal, which is real guidance on how to invoke it. It gives no when-to-use/when-not-to-use guidance relative to the several other assignment-creation siblings.

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