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

With no annotations, the description carries the full behavioral burden. It does disclose a genuine trait beyond a plain function: this renders an interactive card with a slider and format selector rather than performing a silent server-side transform. However, it omits whether compression happens client-side, which formats are supported, and any size limits.

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 front-loaded sentence with no filler; the interactive nature and the before/after feedback are stated up front. It is appropriately sized for a widget tool, though the phrase 'compresses an image' mildly restates the tool name.

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 and no annotations, the description should at least clarify the invocation model. It describes the resulting card well but leaves open how the image is provided (no image parameter exists) and never touches the locale parameter, so the definition is adequate but incomplete for correct invocation.

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?

The single parameter (locale, enum en/zh, default en) has 0% schema description coverage and is never mentioned in the description. The only 'format choice' referenced is a UI control inside the card, not the locale parameter. The description does not compensate for the coverage gap.

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 states a concrete verb and resource ('compresses an image') and goes further by enumerating the card's contents: quality slider, format choice, before/after sizes. It is distinguishable from siblings like image-to-base64 or color-studio. It stops short of explicitly contrasting itself with those alternatives, so it lands at 4 rather than 5.

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 usage is only implied — an agent can infer it should render this card when the user wants to compress an image, but there is no explicit when-to-use statement, no prerequisites, and no routing away from siblings. Notably absent is any guidance on how the image itself is supplied, which is the main invocation ambiguity.

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