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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely non-structured behavior: it is metadata-only, it costs 10 free calls/day then $0.002/call, and payment can flow through x402 in params._meta or an X-API-Key. That billing/rate-limit disclosure is the kind of context an agent cannot get from the schema.

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 the returned fields, then the scope boundary, then pricing — a sensible order. The field enumeration is dense but each item is informative; the trailing '[served by tools.moneytools.dev]' is the only near-dead weight.

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 one simple parameter and an existing output schema, the description need not explain return values, and the pricing/scope notes fill the remaining behavioral gaps. What is still absent is any failure-mode hint (non-HTML pages, unreachable URLs), which matters for an openWorld fetch tool.

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?

There is a single required 'url' parameter with full schema description coverage, so the schema already does the work and the baseline of 3 applies. The description adds nothing about URL format, redirects, or whether non-HTML targets are accepted.

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 the exact extraction target and enumerates the fields it returns (title, canonical, OG/Twitter cards, JSON-LD types, feeds, word count) plus a diagnostic ('what's missing for link previews'). The line 'Metadata only, not page content' carves out scope against content-fetching siblings, though it never names a specific sibling like url_parse_clean to route between 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?

Usage is only implied: the field list and the 'what's missing for link previews' clause suggest preview/debugging use cases, but there is no explicit when-to-use, when-not-to-use, or alternative named. The one concrete context given is commercial (free tier vs paid) rather than situational.

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