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

With no annotations provided, the description carries the full disclosure burden and fully delivers: format-specific handling (PNG/JPEG embedded untouched, others re-encoded), page-geometry defaults (nothing scaled/cropped/letterboxed), rate ceilings (100 files, 50MB, 20 calls/hour/IP), explicit failure mode (HTTP 400 naming the offending file, never a blank-page substitution), REST-vs-MCP output differences, and an expiring-storage-link policy. This is exceptional transparency for an unannotated tool.

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 core purpose is front-loaded in the first sentence, and every subsequent sentence contributes a distinct piece of non-redundant information: format conversion rules, PDF splicing, page sizing, rate limits, error behavior, output delivery, and the fileUrls prerequisite. The description is long (~170 words) but the tool is genuinely complex; the density is justified, though its sheer volume and run-on structure prevent a 5.

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?

Everything an agent needs to call this correctly is present: accepted input formats and their treatment, the mandatory fileUrls-in-own-storage mechanism and how to mint them, per-call and per-IP ceilings, failure semantics, and the return value (raw bytes over REST, persistent-link over MCP). Given that no output schema exists, the description's coverage of the output shape is essential — and provided.

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 100% and both parameter descriptions in the schema are already rich (margin units, pageSize geometry including point dimensions). The description adds contextual framing — default pixel-dimension pages, centering on a fixed portrait sheet — that links the params to the assembly workflow, but it introduces no new parameter semantics beyond what the schema already documents. 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?

Opens with a precise verb+resource+behavior statement: 'Assemble pictures into one PDF, a page per picture, in the order supplied.' It is immediately distinguishable from the PDF-manipulation siblings (merge_pdf, split_pdf, compress_pdf) by being the image-to-PDF direction, and it reinforces the distinction by describing the mixed-input PDF-splicing behavior.

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 description gives clear prerequisites and constraints an agent must honor: files must be fileUrls inside razi.pro's own storage, minted by POSTing to /api/v1/tools/execute first, external links are refused, and MCP carries no attachments. This effectively tells the agent how and when to invoke the tool, but it never names sibling tools or states explicit when-not-to-use conditions, so it stops short of a 5.

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