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

Annotations already declare read-only, idempotent, and non-destructive behavior. The description adds minimal behavioral context—only that it lists definitions—but doesn't disclose details like pagination or response structure. Since annotations cover the safety profile, a baseline 3 is appropriate.

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 a single, front-loaded sentence that directly states the tool's purpose without any filler or redundant information. Every word earns its place.

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 list tool with one parameter and an output schema, the description is largely sufficient. It mentions the entity types and the nature of the result (definitions). It doesn't mention pagination or ordering, but the output schema likely covers return structure, so the description is adequately complete.

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?

The schema fully documents the single parameter (entityType) with an enum and description. The tool description repeats the entity examples but adds no new meaning beyond the schema. With 100% schema coverage, 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?

The description clearly states the tool lists custom field definitions, with a specific verb ('List') and resource ('custom field definitions'), and scopes them to CRM entities. It distinguishes from siblings like get_custom_field (singular) and get_custom_field_values, making the purpose 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?

The description provides clear context by specifying the entity types (account, contact, deal, or booking) for which the tool applies. It doesn't explicitly name alternatives or exclusions, but the context implies when to use it (when you need field definitions for a given entity type), earning a 4 rather than a 5.

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