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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds one genuinely new behavioral fact — 'Every file carries its credit inside' — but the 1024 px cap and 20-item batch limit merely restate schema constraints (maximum/maxItems), so added value is thin.

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 short sentences with no waste; the format/size information and the batch capability are front-loaded. The phrasing 'A code as PNG' is slightly telegraphic, but it stays efficient.

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 required parameters, the description should carry more: it does not say what happens if both code and codes are supplied, what the returned file reference looks like, or what errors occur on an invalid code. The credit note partially fills the output gap, but the definition is only adequate for a 4-parameter tool.

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%, so the description must compensate. It explains format options (PNG/SVG/WebP), a size bound, and that codes triggers multi-render, but it omits the default values (256, png), the code string format (10 alphanumeric chars plus optional 6 hex), and the relationship between 'code' and 'codes'.

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 conveys that a code is turned into an image file (PNG/SVG/WebP) at a given size, which implies rendering, but it never states the verb+resource explicitly (e.g., 'render an avatar'). It also does nothing to separate this from siblings like avatar_for_name, random_avatar, or create_avatar, so an agent must infer the distinction from names alone.

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 only guidance is 'Pass codes to render several in one call (up to 20)', which explains the batch option but not when to choose render_avatar over avatar_for_name or random_avatar, nor when not to use it. No prerequisites, no exclusions, no alternatives named.

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