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

With no annotations provided, the description carries the full burden of disclosing behavior, but it discloses nothing about side effects, output format, units, or any operational characteristics. The text 'Mass of neutron.' is purely nominal and gives no insight into what the tool does when invoked. This is a complete absence of behavioral 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 very short and contains no verbose filler, but it is structurally redundant: 'Neutron Mass' and 'Mass of neutron.' repeat the same idea. It is appropriately sized for a trivial tool, yet the redundancy and lack of functional info prevent a higher score.

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 tool with no output schema, the description should at least state what value is returned and in what units. It only restates the concept of neutron mass, leaving the agent uncertain about return format or precision. The simplicity of the tool does not excuse the complete absence of return-value context.

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 has zero parameters, so the empty schema fully covers the parameter space and the description need not explain any arguments. Per the baseline for zero-parameter tools, a score of 4 is appropriate even though the description adds no parameter 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 'Neutron Mass: Mass of neutron.' is essentially a tautology that restates the tool name without adding a verb or functional action. It identifies the resource (neutron mass) but does not specify whether the tool returns, calculates, or validates it. This provides no meaningful clarity beyond the name itself.

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 offers no guidance on when to use this tool versus alternatives like x402-proton-mass or x402-electron-mass. There is no context about use cases, exclusions, or selection criteria. An agent is left to infer usage solely from the tool name.

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