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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds valuable context beyond annotations by specifying the workspace scope, the required permission (custom_fields:read), and the notable return detail (ready-to-use token), which enriches the behavioral understanding.

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 exceptionally concise: two sentences. The first sentence front-loads the primary purpose and unique value (token), the second adds permission and an API reference link. Every clause contributes necessary information with no redundancy.

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 get-by-id tool with a single parameter, an output schema, and comprehensive annotations, the description fully covers what an agent needs: the resource scope, the distinctive return value (token), and the required permission. There are no significant gaps in context for correct invocation.

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 input schema provides 100% coverage for custom_field_id with 'The custom field identifier.' The description adds that the field comes from the authenticated workspace, giving some contextual meaning, but does not add parameter-specific semantics like format, example values, or relationships. Baseline 3 is appropriate given the high schema coverage.

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 'Returns one custom field from the authenticated workspace' and uniquely highlights the inclusion of the 'exact ready-to-use email personalization token,' distinguishing it from the sibling custom_fields_list. It specifies the action (returns), resource (custom field), and scope (authenticated workspace).

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 conveys clear context: use this to retrieve a single custom field with its personalization token. However, it does not explicitly mention when-not-to-use or name an alternative like custom_fields_list for fetching all fields, so it lacks a direct exclusion/alternative statement.

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