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

With only destructiveHint=false provided, the description adds useful behavioral detail: it returns the field's slug, shows how that slug is used in update_lead via custom_fields, and explains the text interpolation syntax. It does not cover permissions, rate limits, or duplicate-name handling beyond what is in the schema.

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 short, front-loaded with the core action, and uses its remaining clauses efficiently to cover return value, downstream integration, and the deletion alternative.

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 low-complexity, one-parameter creation tool with no output schema and minimal annotations, the description is largely complete. It explains the returned slug and how to use it, though it could mention duplicate-name behavior even though the schema notes uniqueness.

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 name parameter is fully documented in the schema as the label with max 255 and a derived unique slug. The description adds no parameter-specific detail beyond what the schema already supplies, 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?

The description states a specific verb and resource: 'Add a custom field to the account's leads.' It also distinguishes this tool from siblings by naming update_lead for setting values and delete_setup_item for deletion.

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?

It gives a clear alternative for removing the field ('delete one with delete_setup_item') and explains downstream usage in update_lead and text templates. However, it does not explicitly state when to create a new field versus using existing tags, stages, or other setup items.

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