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

Annotations already declare readOnlyHint=false, destructiveHint=true and openWorldHint=false, so the agent knows this is a mutating, non-open-world call. The description adds the plan quota, a genuine constraint not present in annotations, but it never explains what makes the operation 'destructive' or what permissions are needed. With annotations carrying the safety profile, this is adequate but not rich.

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, zero filler, with the core action and supported types front-loaded and the quota caveat trailing. Every clause earns its place.

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 4-parameter mutation tool with no output schema and low schema coverage, the description covers what can be created but not what is returned (e.g., the new field's ID), permission requirements, or behavior on cards that already have the field. An agent could call it correctly but would be guessing at the response and side effects.

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 only 25% – just the 'options' parameter is documented, and boardId/name are bare. The description partially compensates by restating the type enum values and the 'up to 20 options' constraint, but adds nothing about boardId or name semantics, leaving half the meaningful parameters undocumented.

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+resource ('Adds a custom field to a board's cards') and enumerates the five supported field types, which lets an agent separate it from siblings like create_label or create_list without opening the schema. It does not explicitly name an alternative, but the field-type enumeration does the differentiating work.

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?

There is no guidance on when to use this versus update_custom_field or the other create_* siblings, and no prerequisites or when-not conditions. The free-plan quota ('3 per board') is a useful constraint but is a limit, not usage guidance.

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