update_message_flags

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

The description adds valuable behavioral context: the tool verifies the server applied the flags and returns 'notApplied[]' for silently dropped flags. Annotations only provide destructiveHint=false, so this extra transparency about verification and partial-application behavior is meaningful, though more detail on side effects could be included.

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?

The description is concise (three sentences) and front-loaded with the core action and verification behavior. It then provides usage guidance and alternatives without unnecessary detail. Every sentence earns its place.

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 tool with moderate complexity, the description covers purpose, usage context, alternatives, and return behavior (notApplied[]). No output schema exists, so the description's mention of the returned notApplied list fills the gap. It is complete enough for an agent to select and invoke the tool correctly.

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%, with each parameter already described in the input schema. The description adds minimal new parameter semantics beyond mentioning 'arbitrary IMAP flags' and giving an example, which aligns with schema examples. Baseline 3 is appropriate since the schema carries the semantic load.

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?

The description clearly states the tool's function: 'Add or remove arbitrary IMAP flags on a single message, then verify the server applied them.' It distinguishes itself from siblings by explicitly mentioning mark_email_read / star_email as alternatives for common flags and bulk_update_flags for multi-message updates.

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 explicit usage guidance: 'Use for custom IMAP flags (e.g. \Answered) or when mark_email_read / star_email don't cover the flag you need' and 'Prefer bulk_update_flags to update flags across multiple messages at once.' This tells the agent when to choose this tool over alternatives.

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