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

With no annotations, the description carries the full burden and does most of it well: it discloses the 100-ASIN cap, the credential behavior (user's saved Keepa key, otherwise a shared key that consumes daily scan credits), the premium gating, and the async pattern (returns job_id, poll get_a2a_finder_status). It does not cover failure modes or what happens when credits run out, which keeps it short of a 5.

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?

One dense paragraph, front-loaded with the action and its purpose, then constraints, then the return/poll contract. Every sentence earns its place; the parenthetical country example is the only mildly redundant element.

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 two-parameter async job starter with no output schema and no annotations, the description supplies exactly what is missing: the input cap, the credential/credit implications, the premium gate, and the job_id/polling return contract. An agent has everything needed to call it and follow up correctly.

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% with two parameters, so the description must compensate and largely does: it specifies the 100-item limit on `asins`, and explains `countries` as a list of country codes with an example (["UK","DE","FR"]) and the default-to-all behavior. It adds real meaning beyond the bare `array<string>` schema, though it never states whether country codes are ISO-2/ISO-3 or what a valid ASIN format is.

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 ('Start an A2A Finder scan') and then defines the domain term in-line: check a list of ASINs for profitable Amazon-to-Amazon flips across marketplaces. That definition also distinguishes it from the sibling scan starters (start_reverse_source_scan, start_wholesale_scan) without needing to name them.

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?

Usage context is implied rather than stated: the agent can infer this is for Amazon-to-Amazon arbitrage between countries, and it learns the action is a 'Premium feature' and that credits may be consumed. There is no explicit when-to-use/when-not-to-use guidance or a named alternative for adjacent scan types, so this stays at the minimum-viable level.

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