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

Annotations already establish the safe read-only, idempotent profile. The description adds useful behavioral context beyond them: it discloses a call-order requirement and states the return content ('required fields and their types'), which is especially valuable because no output schema exists.

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?

The description is front-loaded with the action and the critical call-order instruction. It is efficient overall, though the supported-type list duplicates the schema's enum-like descriptions rather than adding new information.

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 simple one-parameter read-only tool with rich annotations but no output schema, the description supplies the essential missing pieces: what the tool returns and when to call it. An agent has enough information to invoke it correctly.

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 single segment_type parameter is already fully documented in the input schema. The description repeats the supported-type list but adds no syntax, format, or validation semantics beyond what the schema provides, so the baseline 3 is appropriate.

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 states a specific verb ('Get') and resource ('schema for a segment type'), and distinguishes the tool from siblings by explaining it retrieves field metadata rather than creating or updating segments. The supported-type list makes the resource scope unambiguous.

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 clear usage context with 'CALL THIS FIRST before creating/updating segments,' which routes the agent appropriately relative to segment_create and segment_update. It does not explicitly name those sibling tools or state when not to use this tool, so it stops short of a full 5.

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