mpp_similar_finderFind domains similar to a given domain using MPP (Machine Payments Protocol). Pay-per-request, no API key required.
| Name | Required | Description | Default |
|---|---|---|---|
| domain | Yes | The domain to find similar domains 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 declare readOnlyHint and openWorldHint, and the description adds meaningful behavioral context beyond them: the cost model ('Pay-per-request') and authentication requirement ('no API key required'). These are useful traits that an agent needs to know before invoking the tool, and there is no contradiction with 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 two short sentences with no filler. The primary purpose is front-loaded, and the payment/auth details are placed second for helpful context without bloating the description.
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 one-parameter lookup with an output schema and annotations, the description covers the essential call context including billing and auth. It does not explain what 'similar' means or define result limits, but the output schema is likely to cover return structure, so the missing details are minor.
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 'domain' parameter already has a clear description in the schema. The tool description does not add significant extra meaning beyond restating the domain as the input, so the baseline of 3 is appropriate.
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 uses a specific verb ('Find') and resource ('domains similar to a given domain'), and explicitly identifies the MPP protocol, which distinguishes it from the sibling similar_finder. The purpose is immediately clear and not a tautology.
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 gives context about the billing model and authentication ('Pay-per-request, no API key required'), which implies a reason to prefer this tool over non-MPP siblings, but it does not explicitly state when to use it versus alternatives or any exclusions. The usage guidance is left to inference.
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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