Create a new contact list in MailerCloud.
| Name | Required | Description | Default |
|---|---|---|---|
| name | Yes | List name | |
| dry_run | No | Show what would be created without creating anything | |
| list_type | No | List type (number); leave it out for a regular list (1) |
Changes observed during successful MCP inspections.
Input schema / properties / list_type / descriptionPrevious value: -"List type (number),required"New value: +"List type (number); leave it out for a regular list (1)"Input schema / properties / name / descriptionPrevious value: -"List name,required"New value: +"List name"Input schema / requiredPrevious value: -[
- "name",
- "list_type"
-]New value: +[
+ "name"
+]Input schema / properties / api_keyRemoved value: -{
- "description": "MailerCloud API key",
- "type": "string"
-}Input schema / properties / dry_runAdded value: +{
+ "description": "Show what would be created without creating anything",
+ "type": "boolean"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare write semantics (readOnlyHint=false, idempotentHint=false, destructiveHint=false, openWorldHint=true). The description adds nothing beyond restating the title: it doesn't say whether duplicate names are rejected, whether creation is reversible, or how dry_run behaves. For a mutating, non-idempotent tool, that is a real gap.
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?
A single front-loaded sentence with no filler. It is appropriately sized, though its brevity reflects under-specification rather than tight editing.
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 non-idempotent creation tool with a dry_run flag and no output schema, the description should explain what gets created, what dry_run returns, and duplicate-name behavior. Nearly all of that is absent, so an agent must infer behavior from the schema alone.
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 100%, so all three parameters are documented structurally, and the baseline is 3. The description itself contributes no extra meaning about name constraints, valid list_type values, or the preview semantics of dry_run.
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: 'Create a new contact list'. Clear enough to distinguish from delete_list and update_list. However, it does nothing to separate it from sibling creators like create_segment, create_tag, or create_custom_field, so the agent gets no resource differentiation beyond the name itself.
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?
No indication of when to use this versus alternatives, no prerequisites, and no mention of what to do if a list with the same name already exists. The existence of a dry_run parameter (only in the schema) suggests a preview workflow that the description never surfaces.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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