Inxmail MCP

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

With no annotations provided, the description carries the full burden, disclosing the read-only nature, return format (block date/email if found, 'not blocked' if not), and specific resource accessed (hard-bounce blocklist). Minor gap on rate limits or caching behavior.

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?

Three well-structured sentences: purpose, return values, and usage guidelines. Zero redundancy—every sentence provides distinct value not available in structured fields.

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 lookup tool with 1 parameter and no output schema, the description is complete. It compensates for missing output schema by detailing the response format, and adequately covers scope and siblings for proper agent selection.

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% with the email parameter fully documented as 'Email address to check'. The description references the email but does not add semantic details (format, case sensitivity) beyond the schema. Baseline 3 appropriate for high schema coverage.

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 explicitly states the action ('Check'), resource ('hard-bounce blocklist'), and scope ('specific email'), clearly distinguishing it from sibling tools like get_blacklist_entry and list_blocklist.

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?

Provides explicit when-to-use ('for a single-email lookup') and names two specific alternatives with their use cases ('use list_blocklist to browse all entries; use check_email_blocked to check both blocklist and blacklist at once').

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