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

With no annotations present, the description carries the full behavioral burden, but it discloses nothing about determinism, expected output (a scalar? with units?), or the underlying relation used. It is a pure computation, so a brief note on formula and units would have closed the gap; none is provided.

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 text is a single front-loaded fragment with zero filler, so nothing is wasted. However, it is under-specified for even a trivial tool, so brevity here is not a virtue but a symptom of missing content.

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 one-parameter calculator with no annotations and no output schema, the description should at least state the formula (E = h·f) and expected result/units. As written, an agent knows the topic but not the contract, leaving it incomplete.

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?

Schema description coverage is 100% (the single 'frequency' parameter is documented, albeit vaguely as 'Frequency to process'). Per the baseline rule, the schema doing the heavy lifting yields a 3 even though the description adds nothing about units (Hz?) or accepted formats.

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 'Photon Energy: Energy of photon' essentially restates the tool name and title rather than describing an operation. It does not clarify that this computes E from a frequency, nor how it differs from siblings like x402-energy, x402-kinetic-energy, or x402-wavelength. This is the textbook tautology case.

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 when-to-use, prerequisites, or alternatives are given. An agent cannot tell from this text whether to reach for this tool versus x402-energy, x402-wavelength, or x402-planck-constant, all of which sit in the same physics cluster.

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