list_messages

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

With zero annotations, the description carries the full behavioral burden. It does useful work by disclosing that only headers are returned (not bodies), that results are ordered newest-first by a stable identifier, and that output is capped by a configured maximum. It omits permission requirements, pagination/offset behavior, and what happens when the cap is hit.

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?

A single front-loaded sentence with no filler, and the most important constraint (headers only, newest first) appears immediately. The density comes at the cost of leaving out information the agent needs, but no sentence is wasted.

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 three-parameter read tool with no annotations, no output schema, and 0% schema description coverage, the definition is under-specified: it never says what fields a 'header' contains, whether folder defaults to INBOX, or what unseen_only does. An agent can call it, but only by guessing at the parameters.

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 0%, so the description must compensate for three undocumented parameters (limit, folder, unseen_only) and it does not — none of the three is explained, and 'max configured cap' actually obscures the limit parameter by suggesting a server-side cap rather than a caller-supplied value. Baseline for three unlabeled parameters would be a 3; the misleading framing pushes it down.

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?

States a specific verb and resource ('List newest message headers') plus the ordering key ('stable IMAP UID'), which lets an agent separate it from read_message (single full message) and search_messages (query-driven). It never names those siblings, so differentiation is inferential rather than explicit.

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?

There is no when-to-use guidance at all: no statement of when to prefer this over search_messages for finding messages, and no mention of when the UID ordering matters. The only usage signal is the word 'newest', which implies a recent-inbox browsing scenario.

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