Watermark a local PDF

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

Annotations already declare non-readOnly, non-destructive, non-idempotent, closed-world. The description adds real value beyond that: it writes a new PDF (input preserved), requires an unencrypted/local file, verifies stamp placement and page geometry, and warns signatures become invalid. It stops short of describing overwrite behavior on output_path or failure modes.

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 purpose, then capabilities, then writes/verification, then the disambiguation caveat. No filler; every clause carries actionable meaning.

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?

No output schema exists, and the description compensates by stating a new PDF is written and placement is verified. Given 9 params and weak schema coverage, the missing semantics for size/color/opacity and output-overwrite behavior are the only gaps; callable information is largely present.

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 coverage is only 33%, but the description cover the distinctive parameters: text (one line, rasterized), first_page_only ('or the first page'), diagonal ('centered diagonal or horizontal'), and tiled ('tiled repeats'). It says nothing about size, color, or opacity, which the schema leaves undocumented too, so partial compensation.

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 ('Overlay one line of rasterized text on ... a local unencrypted PDF') plus scope options (all pages vs first page, diagonal vs horizontal, tiled). It is clearly distinguishable from siblings like abox_image_redact or abox_pdf_protect because it explicitly denies redaction/editing prevention.

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 closing sentence 'A watermark does not redact content or prevent editing' gives an implicit when-not and routes the agent toward redact/protect tools. It also implies a precondition (unencrypted PDF, local paths only) but never names a sibling directly or states when a watermark is the right choice over, say, abox_image_redact.

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