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

Beyond the readOnlyHint/idempotentHint annotations, it discloses the decoded size ceiling, that output is an embedded PDF with resolution warnings, that nothing is persisted or mailed, and that workspace auth is required. These are exactly the side-effect and constraint facts an agent needs and none are in the schema or annotations.

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?

Front-loads the core action and limits, then layers constraints; most sentences earn their place. The telegraphic final clauses ('No external URL fetch, persistence or mailing') are compact to the point of terseness but still informative.

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 so return values need not be explained, yet the description still summarizes them (embedded PDF, warnings). Size, auth, and side-effect posture are all covered; the only real gap is the unmapped format enum, which matters for a tool whose whole job is format-sensitive fitting.

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 for imageBase64 (converted from a raw char limit to a 'maximum 25 MiB decoded' semantic) but only gestures at format via 'small single-sided front, large double-sided front and reverse artwork area' without mapping these to the enum values custom_postcard / pro_postcard_85x55 / postcard_reverse.

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 ('Convert imageBase64 ... to print-ready PDF') and adds the mechanism (website's fitting, orientation and resolution checks). No sibling tool performs conversion or rendering of artwork, so the boundary is unambiguous.

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 clear context for when to use it ('print-ready PDF', fitting/orientation/resolution checks) and useful exclusions ('No external URL fetch, persistence or mailing'), plus the 'Workspace authentication required' precondition. It stops short of naming a sibling alternative or explicitly saying when not to use it, so it is not a 5.

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