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

No annotations are provided, so the description carries the full behavioral burden, and it discloses nothing. It does not say whether delimiters are included in the result, what happens when start/end or open/close are absent, how multiple matches are handled, or what the response looks like.

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 minimal, but this is under-specification rather than conciseness. Repeating the name as both title and body consumes the only two available slots without front-loading any usable information.

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?

With six parameters, zero required fields, no annotations, and no output schema, the description should carry substantial explanatory weight and carries none. An agent cannot determine required inputs, delimiter semantics, or output shape from anything provided.

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 nominally 100% but the schema text is vacuous ("End to process", "Open to process"), so no real semantics reach the agent. The description resolves none of the ambiguity among six parameters, particularly the apparent overlap between start/end and open/close, and between text and input.

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?

"Substring Between: Substring Between" is a pure tautology that restates the tool name twice without stating what the operation does or what it returns. The name hints at an extraction operation, but the description adds nothing beyond it, and there is no differentiation from siblings like x402-substring-after or x402-substring-before.

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 guidance whatsoever on when to use this tool, when not to, or how it relates to the very close siblings x402-substring-after, x402-substring-before, and x402-find. The agent is left to infer everything from the name alone.

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