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

With no annotations, the description must carry the behavioral load. It does add real value beyond the schema: the empty-string return contract and the monetization context ('5 free trial calls per signed wallet') tell the agent something about cost and result shape. It still says nothing about required inputs or response payload structure.

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?

One front-loaded sentence covering purpose and edge case, followed by a short pricing clause. No filler, though the trial-call note is tangential to invocation.

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 simple two-input string tool with no output schema and no annotations, the description covers the core mechanics, the alias overlap, and the empty result. It omits required-ness and any note on how ties/length are reported, which leaves a gap against 0% schema coverage.

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 0% on four parameters, so the description has to compensate. It partially does by mapping 'a/text1' and 'b/text2', signaling that these are parallel aliases for the same two inputs, which is genuinely useful given the four-parameter ambiguity. It does not say which alias is expected or that inputs are required.

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 algorithm and resource ('longest contiguous substring shared by strings') and even states the degenerate result (empty string when nothing is shared). That is enough for an agent to distinguish it from near neighbors like x402-common-prefix or x402-levenshtein, though it never explicitly contrasts itself with them.

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 statement of when to pick this over the many sibling string-similarity tools, and no prerequisites beyond the free-trial line. The only conditional given is an output edge case, not usage guidance.

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