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

No annotations exist, so the description carries the full burden. It does disclose two real behavioral traits: only the first occurrence is used and a missing separator yields an empty string. However it says nothing about error handling, payment/auth mechanics beyond the trial-call note, or which of the overlapping input parameters wins.

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 one-liner with the core behavior first and the trial-call promo appended. Efficient, though the promotional clause is not tool semantics.

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 pure-function string tool this covers the core behavior adequately, but with no annotations, no output schema, and zero parameter documentation, the duplicated text/input parameters remain an unexplained gap.

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?

Three parameters with 0% schema description coverage, and the description never explains them. It gives no clue why both 'text' and 'input' exist or how they relate, leaving the most confusing part of the schema entirely undocumented.

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 and resource: returns the text after the first occurrence of a separator, plus the empty-string edge case. It distinguishes itself functionally from substring-before/substring-between, 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?

No when-to-use guidance, no conditions, and no mention of the closely related x402-substring-before and x402-substring-between tools that an agent would need to disambiguate against.

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