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

Annotations already declare a non-read-only, non-destructive, non-open-world mutation, so the safety profile is covered. The description adds one genuinely new behavioral fact not in the annotations or schema: an omitted/empty workspace_id performs the inverse move. It says nothing about what happens if the workspace id is invalid, whether the mailbox must be unassigned first, or any permission requirement.

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?

Two short sentences, no filler, with the primary action first and the edge-case rule second. Nothing could be removed without losing information.

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 two-parameter tool with full schema coverage, annotations, and no output schema, this is close to sufficient: an agent knows what it does and what the empty case means. Minor gaps remain around failure modes (unknown workspace id, mailbox already assigned elsewhere), which matter for a mutation but are not critical here.

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%, so the baseline is 3. The description exceeds that by documenting the semantic effect of omitting workspace_id entirely, which the schema only describes as 'Workspace id from list_workspaces' without explaining the empty case. The email parameter is left to the schema, which is fine.

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: 'Put a mailbox in a client workspace.' That is unambiguous and distinguishable from siblings like create_workspace, rename_workspace, or list_mailboxes. It stops short of explicitly naming which sibling performs a related-but-different operation, so it lands at 4 rather than 5.

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 second sentence gives an explicit rule for the reverse operation: omit or empty workspace_id to return the mailbox to 'My mailboxes.' That is real usage guidance for the optional-parameter case. There is no guidance on prerequisites (workspace must already exist, mailbox must be connected) or on when to prefer this over, say, creating a new workspace.

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