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

Annotations already cover safety (destructiveHint=true, idempotentHint=true, openWorldHint=true), so the bar is lower. The description adds real behavior beyond that: it is a patch-style update ('pass only fields to change') and it resolves the forward_to/forward_rules precedence, which the annotations cannot convey.

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 sentences, front-loaded with the verb and update semantics, followed by the field list and precedence rule. Dense but every clause carries information; no redundant restatement of the title.

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 an 11-parameter mutation tool with no output schema, the description covers the main ambiguities (partial update, forward precedence) and the schema covers the rest. It omits confirmation of return shape, but no output schema exists so that is acceptable.

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 baseline is 3. The description goes beyond the schema by explaining the forward_rules-vs-forward_to interaction and the precedence rule ('non-empty forward_rules overrides per-rule'), which the schema descriptions do not state as a combined rule.

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 (Update) and resource (sender/inbox) with a clarifying parenthetical, so an agent can distinguish it from create_sender_profile and list_sender_profiles. It does not explicitly name a sibling alternative, but the purpose itself is unambiguous.

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 partial-update guidance ('Pass only fields to change') and a rule for choosing between forward_to and forward_rules, which is genuine usage direction. However, there is no explicit when-to-use vs when-not or reference to an alternative tool for related operations.

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