set_mail_message_flags

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

Beyond the annotations (readOnlyHint=false, idempotentHint=true, destructiveHint=false), the description adds the key partial-update behavior: "Only the flags you pass change; the others keep their current value." It also explains the True/False semantics for each boolean flag, which is genuinely useful behavioral detail not present in the schema.

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 compact and well-organized: a clear one-line purpose, one key behavioral rule, a structured Args list, and a returns statement. Every sentence adds valuable information with no filler or repetition.

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 simple 4-parameter flag mutation, the description covers all parameters, the partial-update behavior, how to obtain the required message_id, and what the return value will be. Combined with the annotations and output schema, no essential information is missing for correct invocation.

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 0%, so the description carries the full burden, and it succeeds. It explains message_id with a lookup instruction, and precisely defines seen, flagged, and answered with their True/False meanings, fully compensating for the schema's lack of descriptions.

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 first line states a specific action on a specific resource: "Set or clear flags on a message: read/unread, starred, answered." This clearly distinguishes it from mail siblings like get_mail_message, send_mail, and move_mail_message, which perform different operations.

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 purpose statement makes the intended use clear, and the Args section gives a useful prerequisite: use list_mail_messages to find the message_id. It doesn't explicitly list excluded alternatives, but no sibling tool plausibly overlaps with setting mail flags, so the context is sufficient.

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