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

With no annotations, the description carries the full burden and does disclose the core algorithm (whitespace tokenization, substring containment) plus a payment/rate-limit note (5 free trial calls per signed wallet). It omits match semantics an agent needs: case sensitivity, whether matching is substring or whole-word, ordering, and duplicate handling.

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?

A single front-loaded sentence states the operation, followed by a short promotional/rate-limit clause. No padding or redundant restatement of the tool name beyond the leading label. Efficient, though the label 'Words Containing:' is mild redundancy.

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 two-parameter tool with 0% schema coverage, zero required parameters, no annotations, and no output schema, the description should clarify which argument is the haystack and which is the needle and what the return looks like. It leaves the parameter mapping and match semantics unresolved, so an agent cannot confidently invoke it.

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 coverage is 0% and neither of the two string parameters ('text', 'input') has a description. The prose implies one holds the text and one the substring, but it never maps those roles to the actual parameter names, and 'input' is an ambiguous name that overlaps conceptually with 'text'. This is a real risk of mis-invocation.

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 names a specific verb and resource: it splits text on whitespace and returns the words containing a substring. That is a concrete, verifiable operation. It does not differentiate itself from related siblings such as x402-find, x402-substring-after, or x402-word-prefix, so it falls short of a 5.

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 statement of when to use this tool versus the many other word/substring helpers in the same namespace (x402-substring-between, x402-word-suffix, x402-find, etc.). Usage must be inferred entirely from the one-line behavior summary, and the free-trial note is about billing, not selection.

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