shelf_list_custom_fields

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds the meaningful 'active' qualifier, telling the agent archived definitions are excluded, but says nothing about ordering, pagination, or return shape.

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?

A single front-loaded sentence with no filler. The scope ('active') and the optional filter appear immediately and 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 two-parameter, read-only list tool with no output schema and safety already covered by annotations, this is close to sufficient. The only gap is the absence of any note on result ordering or pagination for a potentially long list.

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 only 50%: orgId is documented in the schema but categoryId is not. The description compensates by explaining categoryId's semantics — restrict results to definitions applying to one category — which is the one undocumented parameter.

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 gives a specific verb and resource ('List active custom field definitions') with a scope qualifier, which distinguishes it from siblings like shelf_list_tags and shelf_list_categories. It stops short of explicitly naming an alternative sibling, but the resource noun is unambiguous.

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?

'optionally those applying to one category' implies when to pass categoryId, so usage is inferable. There is no explicit when-to-use vs. alternative guidance and no statement of when this tool is the wrong choice.

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