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. It discloses the prerequisite 'Requires SMTP access for the originating account,' which is useful behavioral context. However, it lacks details on permissions needed, rate limits, error handling, or what happens to the original email (e.g., marking as replied). The description doesn't contradict annotations, as none exist.

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 two sentences, front-loaded with the core purpose and followed by a prerequisite. Every word earns its place with no redundancy or waste, making it highly efficient and easy to scan.

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 complexity of a 7-parameter email reply tool with no annotations and no output schema, the description is moderately complete. It covers the purpose and a key prerequisite but lacks details on behavioral traits, parameter usage, or expected outcomes. For a mutation tool with rich parameters, more context would be beneficial to fully guide the agent.

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 description coverage is high at 86%, so the baseline is 3. The description doesn't add specific meaning beyond what the schema provides, such as explaining parameter interactions or usage nuances. It mentions SMTP access, which relates to 'account_id' but isn't detailed. No parameters are explicitly discussed in the description.

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 action ('Reply to an email') and specifies the resource ('email'), distinguishing it from siblings like 'send_email' (new email) and 'forward_email' (forwarding). The phrase 'preserves thread' adds specific functionality that differentiates it from other email operations.

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 implies usage context by stating 'Requires SMTP access for the originating account,' which suggests prerequisites. However, it doesn't explicitly state when to use this tool versus alternatives like 'send_email' for new emails or 'forward_email' for forwarding, nor does it provide exclusions or clear alternatives among siblings.

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