MCP Email Service

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It effectively adds context beyond the input schema: it explains that UIDs are scoped per account for follow-up actions, performs live IMAP fetch, and that failures indicate network or credential issues. This covers key behavioral traits like data scoping, real-time operation, and error handling, though it could mention more about pagination or rate limits.

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 appropriately sized and front-loaded, with three concise sentences that each add value: stating the purpose, explaining UID scoping and account_id usage, and describing fetch behavior and failure causes. There is no wasted text, making it efficient and well-structured.

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 tool's complexity (7 parameters, no annotations, no output schema), the description is fairly complete. It covers purpose, multi-account support, UID semantics, and behavioral aspects like live fetching and error indications. However, without an output schema, it could benefit from more details on return values or format, slightly reducing completeness.

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?

The input schema has 100% description coverage, providing clear details for all 7 parameters. The description adds minimal parameter semantics beyond the schema, only implying the importance of 'account_id' for deterministic actions. Since the schema does the heavy lifting, the baseline score of 3 is appropriate, as the description doesn't significantly enhance parameter understanding.

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 tool's purpose: 'List emails from inbox (supports multi-account).' It specifies the verb ('List') and resource ('emails from inbox'), and mentions multi-account support. However, it doesn't explicitly differentiate from sibling tools like 'search_emails' or 'list_unread_folders,' which prevents a perfect score.

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 provides some implied usage guidance by mentioning 'supports multi-account' and that 'UIDs are scoped to each account—pass account_id for deterministic follow-up actions.' It also hints at when to use it by describing live IMAP fetch behavior. However, it lacks explicit when-to-use vs. alternatives (e.g., 'search_emails' for filtered searches) or clear exclusions, keeping it at a moderate level.

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