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

With no annotations, the description carries full responsibility for disclosing behavioral traits. It merely says 'List all custom fields'—the 'list' implies read-only operation, but it does not mention safety, auth requirements, pagination, or return value structure. This is minimal and lacks the depth expected for an unannotated tool.

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, concise sentence that directly states the tool's purpose. Every word earns its place, and there is no redundant or extraneous 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 no-input list operation, the description is mostly complete. The main shortcoming is the vague 'custom fields' without specifying the parent entity (e.g., contacts vs. opportunities), which would help an agent understand the returned data. Otherwise, the tool's simplicity allows a terse description.

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 tool has zero parameters, so the schema is trivially complete at 100% coverage. The description correctly implies that no arguments are needed, and there is no parameter information to elaborate further.

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 a verb ('List') and a resource ('all custom fields'), making the core function obvious. It distinguishes from sibling getters by naming a unique resource, though 'custom fields' lacks explicit scope (e.g., contact vs. opportunity) which prevents a perfect score.

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?

No guidance is provided on when to use this tool versus alternatives. The description does not mention any prerequisites, related use cases, or exclusions, leaving the agent to infer usage from the name and resource.

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