fastmail_mark_email_flagged

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

With no annotations, the description must carry the burden of disclosing that this is a state-changing operation. 'Flag or unflag an email' clearly states the mutation and its both possible outcomes, and '(star)' adds concrete semantic context. It does not cover permissions or return values, but for a simple boolean toggle these are less critical.

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?

Single sentence of five words plus a parenthetical; every word earns its place. The core action is front-loaded before any clarification.

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 two-parameter tool with full schema coverage, the description plus schema fully specify how to invoke the operation. It does not mention the response shape, but no output schema exists and the operation is simple enough that this omission does not block 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?

Input schema coverage is 100%, and both parameters already have clear descriptions ('The email ID', 'Flag (true) or unflag (false)'). The description only adds the 'star' synonym, which is marginal extra meaning. Baseline of 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?

Description opens with the specific verbs 'Flag or unflag' and identifies the resource ('an email'), then clarifies the meaning with '(star)'. This makes the operation unambiguous even though it does not explicitly contrast with sibling tools like fastmail_mark_email_read.

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 description implies the tool should be used when the agent wants to set or remove the starred flag on an email, but it gives no explicit when-to-use or when-not-to-use guidance. No alternatives are named, so the agent must infer the boundary from the tool name.

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