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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds genuinely non-structured behavior: server-side execution, determinism, and a full payment handshake (402 + PAYMENT-REQUIRED, 0.01 USDC, resend with PAYMENT-SIGNATURE) — that is real operational context. It stops short of 5 by omitting rate limits, failure modes other than 402, and by presenting the payment flow only in Japanese.

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 purpose and return value, then determinism, then the payment mechanics, which is a sensible order and every sentence carries information. Minor deductions for the mixed English/Japanese block and the stray '。。' punctuation, which make it slightly harder to parse than it needs to be.

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?

There is no output schema, so the description correctly spells out the return value (matches, indices, capture groups), and it covers the non-obvious 402/payment path an agent must handle. Combined with 100% schema coverage and safety annotations, an agent has what it needs; only error and rate-limit behavior remain unaddressed.

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 100% (text, flags, pattern all documented with limits), so the baseline is 3. The description adds only the constraint that a single pattern is applied per call, which the schema does not state; it offers nothing about flags syntax or pattern flavor.

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 — 'Apply one regular expression to a text blob on the server' — plus the return shape ('every match with its index and capture groups'). This clearly separates it from siblings like diff, csv-json and url-meta, which transform or fetch rather than pattern-match.

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?

Names concrete use cases ('log triage, field extraction and validation at scale') and the payment procedure needed to actually get a result. It gives no when-not conditions or sibling alternatives, so it falls short of a 5, but the context is clear.

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