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 and discloses: (1) mutation type ('This is a write operation'), (2) return value behavior ('Returns empty response on success'), and (3) scope limitations (manual blocks only). Deducting one point for not specifying error behavior when email is not found or idempotency.

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?

Four sentences with zero waste. Front-loaded with action/purpose, followed by operation type, sibling differentiation with conditional logic, and return value. Each sentence earns its place.

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 single-parameter deletion tool without output schema or annotations, the description is complete. It compensates for missing output schema by specifying the empty response, explains the write operation nature, and clarifies domain-specific distinctions (blacklist vs blocklist).

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 has 100% description coverage ('Email address to remove'). The description references 'email' but does not add semantic details beyond the schema (e.g., format validation, case sensitivity). Baseline 3 is appropriate given the schema completeness.

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?

Description specifies the exact action ('Remove an email'), target resource ('explicit blacklist'), and outcome ('allowing emails to be sent to this address again'). It clearly distinguishes from sibling tools by differentiating 'blacklist' (manual blocks) from 'blocklist' (hard bounces) and referencing remove_from_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?

Explicitly states when to use ('Only removes from the blacklist') and provides the exact alternative for different scenarios ('if the address is also on the blocklist... use remove_from_blocklist as well'). This prevents incorrect tool selection for hard bounces.

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