Email lookup: mail provider, role account, disposable, SPF/DMARC, website.
Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.
{
"id": 1,
"jsonrpc": "2.0",
"method": "tools/call",
"params": {
"arguments": {
"email": "<email>"
},
"name": "email_lookup"
}
}| Name | Required | Description | Default |
|---|---|---|---|
| Yes | Email address to look up |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are supplied, so the description carries the full behavioral burden, and it discloses almost nothing: whether the lookup is passive or makes live DNS queries, whether it is rate-limited, whether results are cached, or what happens for malformed or non-existent domains. The only behavioral hint is the implicit field list.
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?
It is short and front-loaded, which is good, but the terse comma-separated fragments (especially 'SPF/DMARC') read as unexpanded keywords rather than sentences, so the brevity costs clarity rather than earning it.
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?
There is no output schema, so the description should explain the shape of the result, yet it only lists loose attributes without saying whether they are booleans, strings, or nested records, or how missing/unknown values appear. For a one-parameter tool with no annotations that is a substantial gap.
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?
There is a single required parameter and schema description coverage is 100%, so the schema already documents 'email' fully. The description adds no format constraints, domain requirements, or normalization rules beyond that.
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 fragment identifies a specific resource (an email address) and enumerates the attributes it reports: mail provider, role account, disposable, SPF/DMARC, website. That is enough to know what the tool returns, but it never distinguishes itself from the sibling email_verify, which plausibly overlaps.
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?
There is no when-to-use guidance at all, no statement of prerequisites, and no mention of alternatives such as email_verify or dns_lookup even though the description explicitly touches SPF/DMARC, which dns_lookup also covers.
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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