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

Annotations already declare the mutation profile (readOnlyHint=false, idempotentHint=false, destructiveHint=false), and the description adds real context beyond them: 1 credit per call, 5 free calls/month, a 24-hour link expiry, and the shape of the response. It omits whether outputs are retained or cleaned up after expiry and where the 5-call quota is tracked.

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 tight sentences: purpose first, then input constraints, then return value and cost. Every clause carries operational information; nothing is restated from the name or title.

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?

An output schema exists, yet the description still summarizes the return (download_url, size, page count), which is helpful rather than redundant. The one gap is dpi: an agent has no basis to choose a value other than the default.

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 carry parameter meaning. It does well on images_base64 (list of base64 strings, per-item size/pixel caps) but never mentions dpi, which the schema exposes with default 200 and no explanation of its effect on output rendering.

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 plus output format: combine images (PNG/JPEG/WebP) into a single PDF, one image per page. The resource (images) implicitly separates it from merge_pdfs, but no sibling is named, so the agent must infer the boundary.

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?

Usage context is implied by the per-image constraints (15 MB / 40 MP) and the cost note, but there is no explicit when-to-use versus merge_pdfs, and no stated precondition such as 'all inputs must be images; use merge_pdfs for PDFs'.

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