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

The annotations already declare readOnly=true, idempotent=true, destructive=false and closed-world, so the safety profile is fully covered without the description. The description adds value by disclosing the return contents (dated price, option/source evidence, purchase URL), but says nothing about behavior when an ID is unknown, stale, or delisted.

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 no filler: the return payload is front-loaded and the input constraint follows. Every clause 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 one-parameter read tool with complete annotations and no output schema, the description covers what to pass and what comes back. The only meaningful omission is failure behavior for invalid or unknown product IDs, which matters given native-price lookups.

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% and already documents the single productId as case-sensitive and sourced from search_products or find_purchase_candidates, so the baseline is 3. The description adds meaning beyond the schema by ruling out merchant URLs and variant IDs as valid inputs, closing the most likely input error.

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 opens with a specific verb and scope ('Read one exact productId') and enumerates what comes back: dated native price, option and source evidence, and the original issued purchase URL. It is clearly the single-record lookup versus the list/search siblings, though it differentiates mainly by ID provenance rather than by naming a sibling's behavior.

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?

It states where valid inputs come from ('IDs come from returned products') and gives an explicit exclusion ('a merchant URL or variant ID is not a productId'), which is exactly the misuse an agent would otherwise make. It stops short of naming which sibling to call to obtain an ID, leaving that inference to the schema and sibling list.

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