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

With no annotations supplied, the description carries the full disclosure burden. 'Lists' makes the read-only nature reasonably clear, and it explains what custom fields conceptually hold, but it never states the return shape (names vs. ids vs. types), pagination, or whether results are company-wide or user-scoped beyond the single mention of 'company'.

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?

Three sentences, each doing distinct work: what it returns, what the data means, and how to use it in a workflow. The purpose is front-loaded and there is no redundant restatement of the tool name.

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 zero-parameter, read-only list tool with no output schema, the description covers purpose, domain meaning, and workflow. The main gap is that it does not say what identifying information a returned definition carries, which matters because the follow-up set_* tools need either an id or a name.

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?

The tool takes zero parameters, which normally sets a baseline of 4, but the description provides no parameter-adjacent meaning to evaluate and nothing about implicit filtering (e.g., whether results are scoped to a company or inventory vs. unit fields). It is adequate but adds nothing on this dimension.

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 opens with a specific verb and resource ('Lists the reusable custom field definitions') and scopes it to 'the user's company'. The word 'definitions' implicitly separates it from value-reading siblings like get_inventory_item_custom_fields and list_unit_custom_fields, but it never names those siblings, so the differentiation is inferable rather than explicit.

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 concrete when-to-use guidance: 'Call this before setting a field so you reuse an existing field name instead of creating a near-duplicate.' That is a clear precondition tied to the set_* siblings. It stops short of stating when not to call it or naming an explicit alternative tool.

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