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

Annotations already declare readOnlyHint=false and destructiveHint=true. The description adds permission-precondition context, which is useful, but it never explains why a join is flagged destructive or what state change/permissions result from joining. With annotations covering the safety profile, a 3 fits.

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?

Purpose is front-loaded in one sentence, followed by two scannable bullets. Minor redundancy in the repeated 'You need to make changes to a document, but...' phrasing, but no real waste.

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 no explanation. The when-to-use preconditions are covered; the only remaining gap is the unexplained destructiveHint flag, which is a minor omission for a single-parameter tool.

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 the schema itself routes the agent to list-documents for obtaining the UUID. The description adds no parameter semantics beyond that, so the baseline 3 applies.

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 + resource ('Joins a document as a collaborator'), which is clearer than a bare tautology. It does not explicitly distinguish itself from siblings like update-document or create-document-party, but the 'as a collaborator' framing clarifies the effect.

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?

Provides an explicit "Use this tool when" block with two concrete preconditions (no 'document user' yet, or existing 'document user' lacks change permission). It gives clear triggering context but never names an alternative tool or a when-not-to-use case.

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