get_messages

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

Very thorough. It explains the no-op behavior for empty lists, silent dropping of missing ids (partial-results), the "SELECTED" sentinel resolution, and the IMAP fast-path vs AppleScript fallback tradeoffs. The return type is described as a list of message dicts. The annotations (readOnlyHint=true, destructiveHint=false) reinforce that this is a safe read, and the description even covers optional-parameter side effects like headers_only being ignored on the fallback. This is exactly the kind of behavioral disclosure an agent needs.

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 efficient but loses a point for leaning heavily on the schema and a code reference. It states purpose, scope, and relationships to siblings in two sentences. Adjective: compact, though the schema carries much of the behavioral detail. Not verbose enough to be a 5.

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?

Everything an agent needs is present: return format (list of dicts), edge cases (missing ids, empty list, SELECTED sentinel), and fallback behavior. Sibling routing is handled. The output schema understands what comes back. This is complete for a read tool.

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 coverage is 100%, and the schema descriptions are unusually detailed. The 'account' and 'mailbox' parameters get extra context (IMAP fast path semantics) that is not directly inferable from the schema, which adds real value. However, the description text itself doesn't reiterate parameter details — it relies on the schema doing the heavy lifting. A 4 acknowledges the added value from the IMAP fast-path context in the schema, while not being a 5 since the description doesn't extend parameter semantics beyond the schema.

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 states a specific verb ('fetch'), resource ('one or more messages'), and scope ('with bodies'). It also explicitly names the sibling tools it is not — search_messages (metadata-only) and get_thread (thread member ids) — so an agent can distinguish them without opening other schemas.

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?

Names the alternatives to pair with (search_messages and get_thread) and the condition for picking those, which routes the agent. It doesn't state when to use this tool over the IMAP fast path vs fallback, but the parameter docs carry that context, and the pairing tip is the key usage decision.

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