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

Annotations cover the safety profile (readOnly=false, destructive=false, idempotent=false), so the bar is lower, and the description adds real context the annotations lack: the PRO+ feature gate and the differing authorization rules for org-wide (admin/manager) vs project-scoped (project owner/manager) fields. It still omits return behavior and uniqueness constraints.

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?

Purpose is front-loaded in the first clause and the remaining sentences are dense with constraints and no filler. Slightly enumeration-heavy, but every sentence carries operational 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 mutation tool with no output schema, the description covers the key domain constraints (tier, valid types, option requirement, scoping and authorization). It is nearly complete, missing only what happens on success or on a name collision.

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 coverage is 75%, so the baseline is 3. The description largely restates what the schema already encodes — the fieldType/entityType enumerations and the option requirement for DROPDOWN/MULTI_SELECT — adding only the role implications of projectId rather than new syntax or format meaning.

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 ('Create') and resource ('custom field definition') and immediately scopes it with the PRO+ tier gate. It is unambiguous against siblings like update_custom_field_def, list_custom_field_defs, and set_custom_field_value.

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?

Gives concrete selection guidance for the projectId parameter (omit for org-wide vs set to scope to one project) and ties each path to an allowed role. It does not explicitly name the sibling to use for editing or listing, so it falls short of full when/when-not routing.

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