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

Annotations declare idempotentHint and openWorldHint, and the description reinforces determinism ('byte-identical output, safe to re-run') plus two facts not in annotations: the unlicensed watermark footer and the inline application/pdf return format. It stops short of stating auth/permission requirements beyond the key note, so it adds real value without being exhaustive.

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?

Four sentences, front-loaded with the core capability before the determinism, watermark, and routing notes. Every sentence carries actionable information with no padding.

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?

For a single-parameter nested-object tool with an output schema and rich annotations, the description covers the value proposition, determinism, licensing caveat, return format, and sibling routing. Nothing an agent needs to call it correctly is missing.

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% and the single nested invoice object is fully documented in-schema (date format, currency pattern, item constraints), so the description adds no parameter-level detail. Baseline 3 is appropriate when the schema carries the burden.

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 (Generate) and resource (invoice PDF) with scope ('from structured data — no template needed'). It explicitly names the sibling it is not (pdf_fill) and the condition that distinguishes them, so an agent can route without opening either 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?

Gives explicit when-to-use ('when you have invoice DATA and no document') and when-not ('if you already have an invoice PDF or a fillable template... use pdf_fill instead'). The alternative is named with its selecting condition, leaving nothing to inference.

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