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

Annotations already establish readOnly=true, idempotent=true, destructive=false, and closed-world, so the safety profile is covered. The description adds real behavioral context beyond that: the return type (PNG), the one-label-per-call constraint, the use of index for multi-label streams, and the presence of an editor link in the result.

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?

The action and return value are front-loaded in the first sentence, followed by the motivating use case, the per-call constraint, and the output link. Three tight sentences with no filler; every sentence carries distinct information.

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 usefully describes the return (a PNG image plus an editor link). For a read-only render tool with full schema coverage and clear annotations, this is near-complete; only minor output details (e.g., error behavior on invalid ZPL) are 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 the schema already documents all five parameters including the index and dpmm semantics. The description's mention of index for multi-label streams largely restates the schema's 'Label index in the stream', adding minimal new meaning. Baseline 3 is appropriate.

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 (render) and resource (ZPL label code), plus the output form (PNG image). This clearly differentiates it from siblings like zpl_validate or explain_zpl, which inspect rather than render. An agent can tell what it produces without opening the schema.

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?

Explicitly states when to use it: to SEE what ZPL output looks like, since LLMs cannot otherwise verify the visual result. It stops short of naming the alternative tools (e.g., zpl_validate) or stating when NOT to use it, so it's clear context without exclusions.

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