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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuinely non-obvious behavior beyond that: a merged product resolves to the current one, and each shop returns only its best offer with a market-currency conversion. No rate limits or error behavior, but solid added context.

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?

A single dense sentence that front-loads the verb and resource. The long tail enumerating return fields is informative but overlaps the output schema, making it slightly heavier than necessary; still, every clause carries real content.

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 read-only two-parameter lookup with an output schema, the description is complete: it signals single-item scope, id provenance, currency conversion, offer selection, and the merged-product edge case. An agent has everything needed to call it correctly without guessing.

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 both parameters are documented in the schema (market enum with default, product_id format and source). The description only echoes the id concept and gestures at market currency; it adds no syntax or semantics beyond the schema, 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+resource ('Returns one product by its Plendio id') and enumerates the exact payload (specs, per-shop best offer with price/shipping/total, currency conversion, availability, condition, price history, URL). This is unmistakably the single-product detail tool, distinct from search_products and compare_prices.

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?

The description never says when to use this versus siblings or where the product_id comes from; that sourcing hint ('the id field of a search result, or the number at the end of a Plendio product URL') lives only in the parameter schema. Usage is implied by the single-id scope, but no explicit when/when-not guidance is given.

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