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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds that output is served by usesignal.dev (external dependency) and that output includes multiple snippet formats, but the 4000px cap merely restates the schema maximum and no auth or rate-limit context is given.

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?

Two tightly written sentences with the core purpose and return shape front-loaded and the size constraint trailing. No filler or redundancy.

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?

An 8-parameter tool with zero schema descriptions and no output schema needs the description to carry parameter and return detail, and it does not. An agent can grasp the intent but not how to use style, pattern, radius, background or color 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 description coverage is 0% across 8 parameters, so the description must compensate and largely does not. It mentions only width/height, repeating the schema's 4000 maximum, and says nothing about text, color, style, pattern, radius or background semantics — leaving half the parameters undocumented anywhere.

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 ('Create a placeholder image URL') and enumerates the concrete artifacts returned (URL, HTML, Markdown, CSS snippets). This is clearly distinct from siblings like usesignal_generate_qr or usesignal_generate_colors 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?

Gives explicit use contexts — mockups, prototypes, seed data, layouts — which tells the agent when this tool is appropriate. It stops short of naming exclusions or alternative tools, so it is clear context without routing guidance.

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