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

Annotations cover the safety profile (destructive=false, idempotent=true, openWorld=true), and the description adds the cost dimension ('$0.001', 'cheapest real call') plus the cheap-probe-before-parsing workflow, which is genuine context not in the structured fields. It does not contradict readOnlyHint=false (the paid call is a real side effect), though it never explicitly frames itself as a metered x402 call — that detail lives only in the x_payment schema field.

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?

Two dense sentences with zero filler; the value proposition and cost come first, then the routing instruction. Every clause earns its place.

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?

An output schema exists, so return values need not be explained, and the description still previews the payload (pages, metadata, text volume, scan estimate). Purpose, cost, and downstream routing are all covered for a 2-param read 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?

Schema description coverage is 100%, so both url and x_payment are already documented in the schema, including the omit-to-get-payment-requirements behavior. The description adds no parameter-level syntax or format detail beyond that, so the baseline 3 applies.

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 ('PDF facts') and enumerates the exact outputs: pages, metadata, per-page text volume, scanned-or-not estimate. It explicitly positions itself against siblings parse_document, pdf_pages and document_pipeline, so an agent can distinguish it without opening any schema.

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?

'Choose this first for any unknown PDF (cheapest real call); then parse_document, pdf_pages or document_pipeline' gives an explicit ordering rule and names the alternatives that follow. When-to-use and which-sibling-next are both spelled out rather than implied.

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