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

With no annotations provided, the description carries full burden for behavioral disclosure. It states it 'Returns a list,' implying a read-only operation, but doesn't specify if it requires authentication, has rate limits, returns paginated results, or what format the list takes (e.g., JSON array of field objects). For a tool with zero annotation coverage, this is insufficient transparency.

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?

The description is a single, efficient sentence that front-loads the core purpose ('Returns a list...') with no wasted words. Every part of the sentence earns its place by specifying what is returned and for what resource, making it optimally concise and well-structured.

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?

Given the tool's simplicity (0 parameters, no output schema, no annotations), the description is minimally adequate. It states what the tool does but lacks context on usage, behavior, or output format. For a read operation with no complex inputs, this is acceptable but leaves gaps that could hinder an agent's effective use, especially without annotations to fill in behavioral details.

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 input schema has 0 parameters with 100% coverage, so the schema fully documents the lack of inputs. The description doesn't need to add parameter details, and it correctly implies no parameters are required by not mentioning any. This meets the baseline for zero-parameter tools, though it doesn't explicitly state 'no parameters needed,' which would have warranted a 5.

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 clearly states the verb ('Returns') and resource ('list of available test case custom fields'), making the purpose immediately understandable. It distinguishes this from siblings like get_case or get_cases by specifying it returns custom fields rather than cases themselves. However, it doesn't explicitly contrast with all siblings, so it falls short of a perfect 5.

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?

The description provides no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., needing a project context), when it's appropriate (e.g., before creating cases with custom fields), or what siblings might be better for related tasks (like get_case for case details). This leaves the agent without contextual usage direction.

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