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

Annotations already establish read-only, idempotent, closed-world and non-destructive behavior, so the bar is lower. The description still adds useful context beyond them: the 256px ceiling, the deterministic/synthetic nature of the output, and the negative disclosure that no image models, uploaded photos or external assets are used.

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?

Three sentences, front-loaded with what is produced and the size limit, then usage, then the negative capability. Slightly redundant with the title but nothing is wasted.

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-value burden and does say it returns SVG placeholder content. All four params are covered by schema, annotations cover the safety profile, and usage boundaries are stated; only the exact SVG shape/size behavior is left implicit.

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 100%, so seed, size, text and pattern are all documented at the schema level with ranges and enum values. The description only restates the 256px bound and gestures at determinism without adding format or interaction detail, 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 ('Generate SVG placeholder avatar') plus a hard size constraint, so an agent knows exactly what artifact it produces. It does not name any sibling (e.g. generate-fake-data or generate-lorem) to disambiguate within the crowded generate-* family, which keeps it short of a 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?

Gives an explicit positive context ('for prototypes') and an explicit exclusion ('Not suitable for matching a real person's photograph'), which is real routing guidance. It stops short of naming an alternative tool for the photo-matching case, so no sibling redirection.

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