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

Annotations already declare readOnlyHint=false and destructiveHint=false, so the mutation safety profile is covered. The description adds that the lock is for coordination ('so other agents can see this connector is working'), hinting at advisory semantics, but omits whether it is blocking, what happens on contention, permission requirements, and any expiry behavior tied to duration_seconds.

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?

A single front-loaded sentence with no filler or repetition of structured fields. It is efficient, though arguably terse for a coordination tool with a related unlock sibling.

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 and annotations plus a fully-described schema carry much of the burden. Still, for a lock tool with a paired mailbox_unlock and a scoped sibling mailbox_lock_files, the description should clarify advisory-vs-blocking behavior and how the lock is released; that gap leaves it only minimally complete.

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%, so the schema already documents all five parameters including reason, account_id, and duration_seconds. The description adds no parameter-level meaning, 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 and resource ('Lock a whole mailbox') and scopes it to acquiring a lock rather than editing content. The qualifier 'whole mailbox' implicitly separates it from the sibling mailbox_lock_files, though it never names that alternative. The trailing coordination rationale is vague but does not obscure the core action.

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 timing guidance ('before broad edits or uploads'), which implies when a lock is warranted versus narrower operations. However, it never names the alternatives (mailbox_lock_files for individual files, mailbox_unlock for release) or states when-not to use it, leaving the routing decision partly to inference.

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