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

Annotations already declare the safe read profile (readOnlyHint=true, destructiveHint=false, openWorldHint=true), so the description need not restate safety. It adds that the payload carries id/name/type and cites the underlying GET /custom-fields endpoint, but says nothing about pagination behavior or result volume beyond what the schema implies.

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 compact fragments, front-loaded with what is returned, then the usage tip, then the endpoint. Nothing is padded, though the endpoint citation (GET /custom-fields) is arguably redundant for an agent.

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?

With no output schema, the description correctly names the returned fields (id, name, type), covering the main gap. Pagination handling is only implied via the schema's next_page note, but for a simple two-param list tool this is close to 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?

Schema description coverage is 100% — both page and limit are fully documented in the schema, including the 'pass the previous reply's next_page' convention. The description adds no parameter detail, 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 the resource (custom contact fields of the account) and the fields returned (id, name, type), which is specific and actionable. It does not explicitly distinguish itself from the similarly named sendlane_get_contact_custom_fields sibling (per-contact values vs. account-level definitions), leaving that differentiation to inference.

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 sentence 'Use the ids when setting field values' implies the workflow leading to sendlane_set_contact_custom_fields, which is useful routing. However, it never states when to prefer this over sendlane_get_contact_custom_fields, nor any exclusions or prerequisites.

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