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

Annotations already declare destructiveHint=true / readOnlyHint=false, so safety is covered; the description adds genuinely new behavioral context by disclosing the default managed demo (self-signed) certificate versus supplying your own key/cert pair, plus the optional visible signature block. It does not state that the output is a newly modified PDF or how the signed file is returned.

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, front-loaded with the core action, then defaults, then the trigger. The final trigger sentence is mildly redundant but does real routing work; there is no filler or marketing language.

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?

For a 7-parameter mutation tool with no output schema and near-zero schema coverage, the description covers the signing-mode decisions but omits what happens on failure, whether an existing signature blocks signing, and the meaning of reason/location. Adequate but with clear gaps.

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 only 14%, so the description must carry the load and it partially does: it explains key/cert as a base64 PEM pair and visible/name as the visible signature block. reason and location are left entirely undocumented in both schema and description, so the compensation is incomplete.

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 ('Apply a PAdES digital signature to a PDF') with the standard named, which distinguishes it cleanly from the sibling pdf_verify_signature. An agent can tell what this does without opening the schema.

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?

'Use this when the user asks to digitally sign a document' gives an explicit trigger, and the default-vs-own-certificate sentence tells the agent which signing mode to pick. It stops short of naming exclusions (e.g., when to prefer pdf_verify_signature or how it relates to pdf_validate_pdfa).

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