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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered; the description adds the useful non-obvious facts that the call is free, needs no account, and returns pass/warn/fail with the measured value. It does not say what happens on malformed or oversized input, which is the remaining behavioral gap for a validator.

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 passage, front-loaded with the verb and the rule list, then the cost/account note, then the return shape. Every clause carries information; no filler or repetition of the title.

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?

With no output schema, the description carries the return contract and does so ('pass, warn or fail per check with the measured value'), which is exactly what an agent needs to interpret results. Rules like 'zoom size' remain slightly underspecified in how they are measured, a minor gap for a validator.

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?

There is a single parameter with 100% schema description coverage, including accepted formats and the 15 MB ceiling. The description restates 'base64' but adds no format, encoding, or sizing nuance beyond the schema, so 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 and resource ('Checks one image (base64) against Amazon's published main image rules') and enumerates the exact rule set being evaluated. The singular 'one image' plus the rule list cleanly separates it from the sibling check_image_set, which operates on a set.

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 scope statement ('one image', base64 input) makes it clear this is the single-image path rather than the set-level check, and 'Free; no account needed' removes a common pre-call hesitation. It stops short of explicitly naming check_image_set or rate_image as the alternatives, so routing is implied rather than stated.

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