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

Annotations already declare this is a non-read-only, non-destructive, non-idempotent write; the description adds real behavioral context beyond them by disclosing the date-within-parent-trip validation rule and the ordering dependency on segment_get_schema. It does not cover auth/permission requirements or what happens on validation failure, so it is not 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, front-loaded with the action and then the required call order and constraint; each sentence carries distinct information with no repetition of the schema.

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?

Covers the prerequisite, required identifiers, dynamic field source, and a key validation constraint for a create tool with no output schema. It leaves the return value (e.g., the created segment ID for chaining) unstated, which is a minor gap given no output schema exists.

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 coverage is 100%, so the baseline is 3; the description goes beyond it by explaining that `fields` is dynamic and must be derived from segment_get_schema for the chosen segment_type, which the schema only hints at. This meaningfully disambiguates the nested, type-dependent parameter.

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 ('Create a new segment in a trip') and the description's workflow (schema lookup, then trip_id + segment_type + fields) makes clear it creates a single typed segment, distinguishing it from segment_update and batch_segment_create. An agent can identify the operation without opening the 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 a concrete prerequisite sequence ('FIRST call segment_get_schema') and a pre-condition with a remediation path ('dates must fall within parent trip dates; use trip_update first to extend the trip'), which is unusually clear context. It stops short of saying when to prefer batch_segment_create over this tool or any explicit exclusion.

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