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

With no annotations, the description carries the full burden of behavioral disclosure, but it only restates that the tool concerns proton mass. It does not disclose the returned unit, numeric value, precision, or whether this is the rest mass or some other definition.

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 extremely short, but it is not effectively concise because it is redundant: 'Proton Mass' and 'Mass of proton' say essentially the same thing. It lacks any structured detail, and the words do not add meaningful information beyond 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?

There is no output schema, so the description must explain what the tool returns. It fails to specify the unit or value of the proton mass, leaving the agent without enough information to interpret the result correctly.

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 and an empty input schema, so the description is not required to explain parameter behavior. The schema already fully covers this aspect.

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 that this tool is about the mass of a proton, which is a specific resource. However, it does not differentiate itself from sibling constants like electron-mass or neutron-mass, nor does it specify units or precision.

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?

No usage guidance is provided. There is no statement about when to use this tool, when not to use it, or how it compares to related sibling tools such as x402-electron-mass or x402-neutron-mass.

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