update_message_flags

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

The description goes beyond annotations by disclosing that user-defined keywords may be silently dropped by Proton Mail Bridge and that UIDs are per-folder. It also mentions the response reports 'no-op (not applied)' for unapplied flags. However, it does not explicitly confirm idempotency (already in 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?

The description is well-structured: main purpose first, then flag types, then critical caveats. It is not overly long, but some sentences could be condensed. Still, every sentence adds necessary value, making it effective.

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?

Given the complexity of modifying flags and the absence of an output schema, the description provides sufficient context: it covers flag semantics, the Proton Bridge bug, and UID scoping. It lacks explicit differentiation from sibling tools, but overall it is complete for its intended use.

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 descriptions cover all 4 parameters (100% coverage), but the description adds valuable context: flag format (backslash prefix for system flags, no backslash for user keywords), and the UID+folder pair caveat. This extra meaning justifies a score above the baseline of 3.

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 action: 'Add or remove flags on an email message.' It specifies the verb (add/remove), resource (email message), and provides details on system flags and user-defined keywords, leaving no ambiguity about the tool's purpose.

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 implicitly indicates usage for single-message flag management, but it does not explicitly differentiate from sibling tools like 'bulk_update_flags' or 'flag_thread.' No guidance is given on when to use this tool vs. alternatives, which is a notable gap.

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