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

Annotations already declare destructiveHint=true, readOnlyHint=false, and idempotentHint=false, so the mutation/destructive nature is covered. The description adds the 'existing' qualifier (target must exist) and names the exact field being mutated (expiration date), but it does not add context such as authorization needs, notification side effects, or whether the new date must be in the future.

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 description is a single, front-loaded sentence containing exactly the necessary scope: what is updated ('expiration date') and on what ('existing signing assignment'). There is no filler or redundant restatement of the tool name.

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 3-parameter mutation with full schema coverage and annotations already conveying destructive and non-idempotent behavior, the description is nearly complete. It could add one sentence on allowed expiry values or invocation preconditions, but nothing essential is missing for selecting and invoking this tool among the siblings.

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 100% and each parameter has clear schema-level descriptions, so the baseline is 3. The tool description itself adds no parameter-level meaning beyond the schema, which is acceptable because the schema already documents the expiry format (RFC 3339) and the required IDs.

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?

The description uses a specific verb ('Update'), a specific resource ('expiration date of an existing signing assignment'), and identifies the assignment as pre-existing. This clearly distinguishes it from sibling tools like create, delete, send, and verify; no other sibling tool handles expiration changes.

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 operation itself implies the use case (whenever an assignment's expiration needs to change), but the description offers no explicit when-to-use or when-not-to-use guidance and does not mention alternatives or prerequisites beyond the assignment being 'existing'. There is no sibling overlap, so it is not misleading, just implicit.

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