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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description adds one genuine behavioral trait beyond that – the signature keeps its aspect ratio – and states the return format, but says nothing about whether the source PDF is modified, what happens on out-of-range pages, or any size/latency limits for the 10 MB nested caps.

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 densely packed sentences: the purpose and placement semantics come first, the return format second. Both are front-loaded and waste little, though 'Returns the signed PDF as base64' is redundant given the output schema exists.

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 an output schema present, the return value needn't be explained, and the placement coordinate system is fully spelled out. What is missing is edge-case behavior – an invalid page number, a non-PNG signature, or the 20-placement cap – but for a single-purpose stamping tool this is close to complete.

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 67% and the nested placement properties already document x, y, page, and width with the same fraction/top-left conventions the description repeats. The description's only added value is tying width to the preserved aspect ratio, so the baseline 3 for schema-heavy parameter documentation 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?

The description names a specific verb and resource ('Stamp a PNG signature image onto one or more PDF pages') plus the placement model, which clearly separates it from siblings like merge_pdf, split_pdf, or protect_pdf. It never explicitly names an alternative, but the operation itself is distinctive enough that an agent can route to it correctly from the catalog.

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?

There is no when-to-use guidance, no prerequisites (the signature must already be a PNG; the PDF must come from a URL or base64), and no mention of siblings such as images_to_pdf or extract_pdf_text for adjacent tasks. The agent is left to infer context entirely from the tool name and schema.

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