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

With no annotations, the description carries the full burden. It does disclose that this is a fixed constant with no inputs or side effects, which is useful, but it omits return units and any precision or formatting details.

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 short and front-loaded, but it is mildly redundant: 'Earth Mass' is effectively repeated in 'Earth mass constant.' A single, leaner phrasing would be slightly stronger.

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 this is almost sufficient, but because there is no output schema, the description should state the unit or return format. 'Earth mass constant' leaves ambiguous whether the result is in kilograms, Earth-mass units, or some other representation.

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 is empty and there are zero parameters, so there are no parameter semantics to document. The baseline of 4 applies because there is no parameter ambiguity and no need for the description to compensate.

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 identifies a specific physical quantity (Earth mass) and labels it as a constant, so the agent can tell the tool returns a predefined value rather than computing from inputs. However, it lacks an explicit verb like 'returns' and does not contrast with sibling constants such as x402-solar-mass.

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?

There is no explicit when-to-use or alternative-selection guidance. The phrase 'Earth mass constant' implies it should be used whenever Earth's mass is needed, but nothing distinguishes it from the many related physical-constant tools in the sibling list.

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