Look up a Listmonk subscriber by exact email address to retrieve their details; returns a not-found error when no matching address exists.
Look up one subscriber by exact email address and return the same details as get_subscriber_by_id. Returns a not-found error if no subscriber has that address.
| Name | Required | Description | Default |
|---|---|---|---|
| Yes | Subscriber email |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, and the description adds genuinely new behavior: exact (non-fuzzy) matching and a not-found error when no subscriber matches. It does not cover case sensitivity or whether the lookup is rate-limited, but the safety and failure profile is largely 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 sentences, zero filler, with the lookup scope front-loaded and the error contract as a closing clause. Every sentence carries information an agent needs.
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 one-parameter read tool with no output schema, the description covers input scope, return-shape (by reference to get_subscriber_by_id), and failure mode. The only gap is that the actual returned fields are only available indirectly via that sibling reference.
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 single parameter is trivially documented, so the baseline is 3. The description earns an extra point by clarifying that the email must match exactly, which is real semantic information the schema's format=email does not convey.
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 and resource ("look up one subscriber") with a scoping constraint ("by exact email address") and explicitly names the sibling whose output shape it mirrors (get_subscriber_by_id). An agent can distinguish it from get_subscriber_by_id and list_subscribers without opening any schema.
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 exact-match requirement plus the pointer to get_subscriber_by_id implicitly establish when to use which tool (you have an email vs. an ID). No explicit exclusion or prerequisite is spelled out, so it falls short of a full when/when-not statement.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.