Hibp

Check Password

check_password

Read-onlyIdempotent

Check whether a password appears in known breach corpora. Uses k-anonymity: the password is SHA-1ed locally, only the first 5 hex chars leave the worker, and the response is filtered to match the rest. Returns pwned count (0 = not seen). The password itself is never transmitted.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`password`	Yes	Password to check (stays inside the worker)

Output Schema

TableJSON Schema

Name	Required	Description
`pwned`	Yes	Whether password appears in breach corpus
`advice`	Yes	Security advice based on pwned status
`pwned_count`	Yes	Number of times password seen in breaches
`sha1_prefix`	Yes	First 5 hex characters of SHA-1 hash

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedMay 22, 2026

addedInput schema / examples

Added value: +[
+  {
+    "password": "correct-horse-battery-staple"
+  },
+  {
+    "password": "MyP@ssw0rd123"
+  }
+]

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "advice": {
+      "description": "Security advice based on pwned status",
+      "type": "string"
+    },
+    "pwned": {
+      "description": "Whether password appears in breach corpus",
+      "type": "boolean"
+    },
+    "pwned_count": {
+      "description": "Number of times password seen in breaches",
+      "type": "number"
+    },
+    "sha1_prefix": {
+      "description": "First 5 hex characters of SHA-1 hash",
+      "type": "string"
+    }
+  },
+  "required": [
+    "pwned",
+    "pwned_count",
+    "sha1_prefix",
+    "advice"
+  ],
+  "type": "object"
+}

First observedMay 11, 2026

TDQS

A4.4/5.0

Behavior5/5

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

Annotations already indicate readOnlyHint=true and destructiveHint=false, but description adds critical context: password is SHA-1ed locally, only first 5 hex chars sent, password never transmitted. This fully discloses behavioral traits beyond annotations.

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?

Three concise sentences: first states purpose, second explains k-anonymity mechanism, third clarifies no transmission. Every sentence is necessary and efficient.

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?

Given a single parameter, presence of output schema, and clear annotations, the description sufficiently covers purpose, security mechanism, and result format. No gaps identified.

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

Parameters4/5

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

Input schema has 100% coverage with description 'Password to check (stays inside the worker)'. The tool description reinforces that the password remains local, adding semantic meaning beyond the schema's basic description.

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?

Description clearly states the tool checks password against breach databases with specific verb 'check'. It implicitly distinguishes from 'check_password_prefix' sibling by describing full k-anonymity mechanism, but does not explicitly differentiate.

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

Usage Guidelines4/5

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

Provides clear context for when the tool is appropriate (breach checking) and implies privacy-preserving usage via k-anonymity. Does not explicitly mention when not to use or alternatives, but context is sufficient.

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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