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

Annotations already cover the read-only/idempotent safety profile, and the description adds genuinely useful context annotations cannot express: this is a paid call ($0.001 USDC per successful call via x402 on Solana) with an equivalent HTTPS endpoint. That cost/auth detail is material to an agent deciding whether to invoke. It stops short of describing the response shape.

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?

Telegraphic sentence fragments, front-loaded with the resource domain and followed by orientation, conversion, example, and pricing in descending priority. Almost every sentence earns its place; the inches formula is arguably marginal for a mm-based API but supports the conversion claim.

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 two simple parameters and no output schema, the description is close to sufficient — it fixes units (mm), orientation semantics, and shows a concrete result (210 by 297). But it never states the response shape (e.g., width/height fields vs. a formatted string) nor the valid set of name values, which is the one thing an agent must get right to call it successfully.

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 coverage is 0%, so the description must carry the load. It does clarify 'landscape' ('set landscape to swap the sides') and indirectly illustrates the name parameter ('A4 is 210 by 297'), but it never states the accepted name format (A4, B5, C6, DL), case sensitivity, or what the maxLength 8 constraint implies.

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 opening clause names the exact resource domain — ISO 216 A, B and C series plus DL envelope, in millimeters — so an agent knows this is a paper-dimension lookup, not a fit/scale calculation. It never names the closest siblings (paper_fit, paper_scale, envelope_fit), so differentiation is left implicit.

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?

Use is implied by the domain statement and the orientation/conversion notes, which tell you how to read results rather than when to pick this tool. Nothing states when to prefer it over paper_fit or envelope_fit, and no exclusions or prerequisites are given.

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