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

The annotations already declare readOnlyHint, openWorldHint, and idempotentHint=false, but the description adds genuinely useful behavior not in structured fields: the exact credit cost, that actual cost follows the plan, that repeated calls may charge again (consistent with idempotentHint=false), and a warning to treat returned data as untrusted. This meaningfully exceeds the annotation baseline.

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?

It is a tight four-sentence block with the purpose front-loaded, followed by cost, repeat-charge, and safety notes. Every sentence carries distinct information with no filler, though it is terse enough to feel slightly clipped rather than polished.

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, credit-charged retrieval tool with no output schema, the description covers purpose, cost model, and data-trust handling adequately. It stops short of describing the shape of the returned traffic-source composition, which would help given the absence of an output schema and the presence of a returnFields parameter.

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?

With schema description coverage at 100%, the schema already documents q, page, size, month, order, marketplace, and returnFields. The description only reinforces that q accepts an ASIN or keyword, adding little 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?

The description uses a clear verb+resource combination ("Retrieve traffic source composition") and specifies the scope as "for an ASIN or keyword." It does not, however, distinguish this tool from the many traffic-related siblings (amazon_traffic_extend, amazon_traffic_keyword, amazon_traffic_listing_page, etc.), leaving an agent unsure which traffic endpoint is appropriate.

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 hints at input flexibility ("ASIN or keyword") but provides no when-to-use criteria, no prerequisites, and no comparison to the numerous sibling traffic tools. There is nothing telling an agent when this tool is the right choice over amazon_traffic_keyword or amazon_traffic_listing_stat.

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