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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the tool's safe read-only nature is fully covered. The description adds useful context about the grouping categories ('food additives, flavouring agents, food contaminants and veterinary drugs') and the count of 71 classes, but doesn't add much beyond that. No contradiction with annotations.

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, information-dense sentence followed by a short directive sentence. It front-loads what the tool returns, then gives the actionable 'call this to…' purpose. Every clause adds value, and there is no repetition of the title or schema.

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 0 parameters, no output schema, and rich annotations covering safety/idempotency, the description covers what an agent needs to decide to call it and what it will get. It could optionally mention that the output is a controlled vocabulary list with no pagination or filtering needs, but that omission is minor for such a simple lookup tool.

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, so there is no schema burden to compensate for. The description adds meaningful semantics by explaining what the response vocabulary contains—names, examples, grouping categories—and how it relates to another tool's parameter expectations. Since there are no params to document, a 4 is appropriate; it loses one point only because it doesn't describe the return structure in detail.

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 states a specific verb ('List'), a clear resource ('the JECFA functional-class vocabulary'), and a key distinguishing detail ('the 71 technological purposes a substance can be evaluated under'). It even gives examples of class names, so an agent immediately knows what kind of data this returns and can tell it apart from siblings like jecfa_by_functional_class or jecfa_chemical.

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 explicitly says when to call this tool: 'Call this to discover the exact class name that jecfa_by_functional_class expects.' This names the dependent sibling and the precise purpose, giving clear guidance on when to use this vs. other JECFA tools. It also implies that this is a supporting vocabulary lookup rather than a standalone search.

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