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

No annotations are provided, so the description carries the full burden. It does add real behavioral context — the exact mathematical criterion and the trial/pricing constraint ('5 free trial calls per signed wallet') — but it never says whether the result is a boolean, what happens for invalid/non-integer input, or how large values are handled.

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?

Front-loaded with the definition and examples in a single tight sentence; nothing is buried. The leading 'Is Semi Prime:' restates the tool name and the trailing emoji/trial note is slightly noisy, but the core content is efficient.

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 trivial predicate this covers the semantics well, but with no output schema the description should state the return shape (boolean), and with 0% parameter coverage it should say what format 'value' takes. Reasonably complete, with clear gaps an agent would have to guess at.

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?

One parameter at 0% schema description coverage and not marked required. The description clarifies that 'value' is the number being tested for having two prime factors, which adds meaning, but with the schema typing it as a string it gives no guidance on accepted format (decimal string? magnitude limits?). It partially compensates for the coverage gap but not fully.

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?

States a specific verb ('Checks whether') and resource (semi-prime / 'exactly two prime factors counted with multiplicity') and reinforces it with examples (4, 6). The formal definition lets an agent distinguish this from adjacent predicates like is-prime (one factor) or is-sphenic (three distinct primes), though it never names those siblings explicitly.

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?

Usage is only implied: an agent infers this is the predicate to call when it needs a semiprimality test. There is no when-to-use statement, no exclusion, and no reference to neighboring tools such as x402-is-prime or x402-is-sphenic, which is where confusion is most likely.

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