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

Beyond annotations (destructiveHint, openWorldHint), the description discloses the shared multi-caller workspace, that writes reach inboxes other callers created, that changes are visible/editable by later callers, and that the return value is the full updated inbox. It also notes the address is immutable. No contradiction with annotations.

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?

Four tight sentences put the core mutation first, then return value, then shared-workspace warning, then read alternative. Every sentence earns its place and the most important behavioral caveat is front-loaded.

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 mutating inbox tool with an output schema and rich parameter schema, the description covers purpose, return value, cross-caller side effects, and the safe read alternative. Nothing needed to call it correctly is missing.

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%, with rich descriptions of display_name and metadata merge/null behavior, so the description doesn't need to re-explain parameters. It adds the high-level field scope and address-immutability note, but no per-parameter detail; baseline 3 is appropriate.

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?

Starts with the specific verb 'Updates' and names exactly the resource and fields ('one inbox's display_name and metadata'), and explicitly states the address cannot change. This distinguishes it from sibling patch/draft/message/thread tools and from get_agentmail_inbox, so an agent can select it 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?

Provides clear usage context: this is the write path for inbox display_name/metadata, while 'To read without changing anything use get_agentmail_inbox' gives an explicit alternative. It warns about shared-workspace side effects, but it does not explicitly contrast with patch_agentmail_inbox_draft/thread/message; the resource-scoped naming and wording handle that indirectly.

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