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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds real behavioral value beyond that: the server computes the MD5 id from the email, and the underlying GET /leads/{md5(email)} route is disclosed.

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?

Two dense sentences with no filler: purpose and return fields first, then the no-list caveat and the endpoint. Everything is front-loaded and each clause carries information.

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?

Even without an output schema, the description enumerates the returned fields (name, custom fields, timezone, subscribed/opt-in status, tags, dates) and discloses the endpoint, so an agent knows both how to call it and what to expect back.

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% and the schema already labels email as preferred and lead_hash as the 32-char MD5 alternative. The description adds the non-obvious semantic that the MD5 is derived from the lowercased email server-side, clarifying how the two parameters relate.

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 (get) and resource (one lead), plus the lookup key (email address) and the returned fields. It explicitly notes MailBluster has no list-leads endpoint, which separates it from any listing behavior an agent might expect.

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?

Tells the agent this is the way to fetch a single lead and that no list endpoint exists, and identifies email as the preferred identifier over lead_hash. It does not spell out when to prefer this over update_lead for read-back purposes, but the routing context is clear.

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