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

The readOnlyHint=true annotation already tells the agent this is a safe, non-mutating read, so the description's main job is to add beyond that — and it adds essentially nothing (no pagination behavior, no auth requirements, no expected size of the result set). The endpoint string confirms the read but is not new behavioral information.

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?

Two short sentences, front-loaded with the purpose, with zero filler. Nothing could be trimmed without losing 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 zero-required-parameter, read-only list tool with a fully documented schema and no output schema, the description covers the essentials. It nonetheless omits what a returned property record looks like (name/type/id), which would help an agent chain into loops_create_contact_property.

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 enum parameter (all vs custom) is fully documented with its default in the schema. The description adds no syntax or semantics beyond that, so 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?

States a specific verb and resource ("List contact fields / custom properties defined in Loops") and even the underlying endpoint, so an agent can tell it apart from write siblings like loops_create_contact_property. It does not, however, explicitly contrast itself with loops_list_mailing_lists or loops_find_contact, so differentiation is only implicit.

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?

There is no when-to-use guidance, no exclusions, and no mention of alternatives such as loops_create_contact_property for the write path. The only context is the raw REST endpoint, which describes the mechanism rather than the decision.

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