mpp_email_countGet the count of email addresses available for a specific domain using MPP (Machine Payments Protocol). Pay-per-request, no API key required.
| Name | Required | Description | Default |
|---|---|---|---|
| domain | Yes | The domain to count emails for |
| Name | Required | Description | Default |
|---|---|---|---|
| data | Yes |
Changes observed during successful MCP inspections.
Output schema / (root)Previous value: -nullNew value: +{
+ "$schema": "http://json-schema.org/draft-07/schema#",
+ "additionalProperties": false,
+ "properties": {
+ "data": {}
+ },
+ "required": [
+ "data"
+ ],
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already provide readOnlyHint=true and openWorldHint=true. The description adds valuable behavioral context by disclosing the pay-per-request billing model and the lack of an API key requirement, which are not visible in annotations.
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 a single focused sentence that front-loads the operation and resource, then efficiently adds the key MPP and billing context. No words are wasted.
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 simple tool with one fully documented parameter, read-only annotations, and an output schema present, the description covers the essential context: what is counted, the domain scope, the protocol, the cost model, and authentication. Nothing critical is missing.
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?
The input schema fully describes the single 'domain' parameter with a pattern and description, so schema coverage is 100%. The description only restates that the count is 'for a specific domain', adding no new parameter-level detail beyond the schema.
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 a specific verb ('get') and resource ('count of email addresses available for a specific domain'), and adds the MPP context. It is understandable and distinct from generic counting, though it does not explicitly name the sibling 'email_count' as an alternative.
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 through 'using MPP', 'Pay-per-request', and 'no API key required', suggesting this is for MPP-based billing. However, it does not explicitly state when to use this tool instead of non-MPP siblings like 'email_count'.
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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