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

Annotations only declare readOnlyHint and openWorldHint=false; the description adds real behavior the annotations cannot: a fixed $0.002 USDC per-call cost and the exact x402 challenge/retry protocol. It also names the comparison outputs. It stops short of 5 because it does not say what the response payload looks like (counts, per-SKU delta structure) despite there being no output 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?

Four short sentences, zero filler: purpose first, outputs second, scope constraint third, payment mechanics last. Every sentence carries information an agent needs.

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 no-output-schema, four-parameter diff tool the description covers purpose, comparison semantics, cost, and the auth/payment loop, which is most of what an agent needs to call it. Gaps remain on response shape and on how the optional before/after vs. beforeCsv/afterCsv inputs interact when both or neither are given.

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 100%, so the schema already documents sku, price, currency, availability, and the CSV alternatives. The description adds the matching key ("by SKU") and that price deltas are currency-aware, which is genuine semantic value, but it leaves ambiguous whether before/after and the CSV variants are mutually exclusive or mergeable. Baseline-plus, not a 4.

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 ("Compare two caller-supplied JSON or CSV product snapshots by SKU") and enumerates the outputs: added, removed, changed products plus currency-aware price deltas. That distinguishes it cleanly from siblings like schema_diff and product_title_normalize without requiring a schema read.

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?

Makes the operating context explicit: snapshots are caller-supplied, "No scraping", so the agent knows it must already hold the data. It also gives a concrete conditional flow for the payment path (no payment returns x402 requirements; retry with a header or _meta field). It does not name a sibling alternative or exclusion, so it stops short of a 5.

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