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

Annotations already declare readOnlyHint=false, idempotentHint=false, destructiveHint=false and openWorldHint=true, so the write/non-idempotent profile is covered. The description's "write operation" line largely repeats that, though the POST path adds a small amount of context. It does not disclose auth requirements, what happens on duplicate names, or failure behavior.

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 core action and then the constraint, with no filler. The "Limitations:" label is slightly odd for what is really a required-parameter note, but the text is compact and earns its space.

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 an 11-parameter mutation tool with no output schema, the description covers the purpose and the two enum-bearing required params. It omits guidance on the auth parameters (api_token/app_password/access_token), the multi-workspace account_id requirement, and any return/error behavior, leaving meaningful gaps for an agent configuring the call.

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 55% with 11 parameters, several of which (name, color, notes, cf_index, api_token, access_token, app_password) have no schema description. The description only restates that value_type and filter_object_class are required, which the schema's required array already conveys, and the object-class list duplicates the enum. It adds essentially nothing beyond the structured fields.

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 (creates a new custom field) and scopes it by naming the object classes it can attach to (task, project, event, user, customer), which distinguishes it from siblings like create_enum_option and update_custom_field. The API endpoint is also given, so an agent knows exactly what operation this is.

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 states that this is a write operation and that value_type and filter_object_class are required, which is implied usage guidance for creating a field. However, it never says when to choose this over update_custom_field, create_enum_option, or how it relates to list/get custom field tools, so no alternatives or exclusions are given.

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