RelayShield Scam Checks

Check an email against known data breaches

check_breach

Read-only

Checks whether an email address appears in known data breaches. Provide email. Returns the number of breaches found with the named sources behind each; a count of zero means no breaches were found in the corpus, not that the address is safe. Read-only: it only looks up breach records. Requires the RELAYSHIELD_API_KEY environment variable; without it, the tool returns setup instructions instead of calling the API.

Tool call template

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": "check_breach"
  }
}

Input Schema

Name	Required	Description	Default
`email`	Yes	Email address to check. Case-insensitive.

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed4 schema fields changedNov 11, 2026

removedInput schema / properties / email / format
```
Removed value: -"email"
```
addedInput schema / properties / email / title
```
Added value: +"Email"
```
addedInput schema / title
```
Added value: +"check_breachArguments"
```

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "result": {
+      "title": "Result",
+      "type": "string"
+    }
+  },
+  "required": [
+    "result"
+  ],
+  "title": "check_breachOutput",
+  "type": "object"
+}

First observedSep 30, 2026

TDQS

A4.1/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the annotations' readOnly/destructive profile, the description discloses the return shape (count plus named sources), an important interpretive caveat (zero does not mean the address is safe), and the authentication requirement with its exact failure behavior when RELAYSHIELD_API_KEY is absent. That is the kind of operational context annotations cannot carry.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Four short sentences, ordered usefully: purpose, input, output meaning, safety and auth. Every sentence carries distinct information, and the most decision-relevant caveat about zero counts is not buried.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

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 an output schema, this covers everything an agent needs: what it queries, what comes back, how to interpret a null result, that it is safe to call, and what breaks without credentials. Nothing material is left unaddressed.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and the single parameter already documents case-insensitivity, so the description's "Provide `email`" adds nothing new. Baseline 3 applies where the schema does all the parameter work.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

"Checks whether an email address appears in known data breaches" gives a specific verb (checks) and a well-scoped resource (breach corpus membership), which reads distinctly from generic siblings like check_email or check_link. It stops short of explicitly naming an alternative, so an agent must infer that routine email validation belongs elsewhere.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is implied by the scope statement rather than stated: the tool is for breach-corpus lookups, and the zero-count caveat tells the agent how to read a negative result. There is no explicit when-not-to-use guidance or reference to a sibling tool for adjacent email checks.

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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