DiffiCat

Capture screenshot

capture_screenshot

Takes a full-page screenshot of one URL, for example to see how a relaunched page or a mobile layout looks. Free 5 times, once per client address, no key needed. The PNG is taken at the given viewport width and returned inline when small, else as links.file to fetch with the jobToken. Call it for a one-off look at a page or a mobile-width check. Do not call it for pages a comparison job covers: the job already stored their screenshots. Example: { "url": "https://new.example/pricing", "viewportWidth": 375 }. Answers with jobId, jobToken, filename, url, dimensions, bytes, links.file and, on a free run, sample and allowanceRemaining.

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": {
      "url": "<url>"
    },
    "name": "capture_screenshot"
  }
}

Input Schema

Name	Required	Description
`url`	Yes	Page to capture (full URL).
`auth`	No	HTTP basic auth for the page.
`visual`	No	Capture rules applied to both sides.
`viewportWidth`	No	Capture width in px.
`idempotencyKey`	No	Retry key: under a prepaid balance, the same value within 24 hours is not charged again and answers DUPLICATE_REQUEST with the first jobId.

Output Schema

Name	Required	Description	Default
`url`	No
`code`	No
`bytes`	No
`error`	No
`jobId`	No
`links`	No
`region`	No
`sample`	No
`payment`	No
`filename`	No
`jobToken`	No
`followUps`	No
`imageSize`	No
`dimensions`	No
`pagesCharged`	No
`allowanceRemaining`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedNov 7, 2026

changedInput schema / properties / idempotencyKey / description

Previous value: -"Optional opaque string a retry repeats: under a prepaid balance the same value within 24 hours is not charged again and answers DUPLICATE_REQUEST with the jobId of the first call."New value: +"Retry key: under a prepaid balance, the same value within 24 hours is not charged again and answers DUPLICATE_REQUEST with the first jobId."

Changed1 schema field changedNov 2, 2026

addedOutput schema / properties / followUps

Added value: +{
+  "items": {
+    "type": "string"
+  },
+  "type": "array"
+}

Changed2 schema fields changedOct 25, 2026

changedInput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

changedOutput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

Changed3 schema fields changedOct 17, 2026

changedInput schema / properties / visual / properties / freeze / properties / clock / description

Previous value: -"Pause timers and the clock after load on both sides; a page that waits on a timer to render may stay empty."New value: +"Pause timers and the clock after load; a page that needs a timer to render may stay empty."

addedInput schema / properties / visual / properties / freeze / properties / clockSeconds

Added value: +{
+  "description": "With clock: seconds the clock runs after load before it stops (1 to 600, default 60).",
+  "maximum": 600,
+  "minimum": 1,
+  "type": "integer"
+}

changedInput schema / properties / visual / properties / masks / description

Previous value: -"CSS selectors of elements hidden on both sites before the screenshot (at most 50, each up to 200 characters). The box is kept, so the layout does not shift."New value: +"CSS selectors of elements hidden on both sites before the screenshot (at most 50, each up to 200 characters). The layout keeps its place."

Changed1 schema field changedOct 16, 2026

addedInput schema / properties / visual

Added value: +{
+  "additionalProperties": false,
+  "description": "Capture rules applied to both sides.",
+  "properties": {
+    "freeze": {
+      "additionalProperties": false,
+      "description": "Switches that stop motion before the screenshot.",
+      "properties": {
+        "animations": {
+          "description": "Stop CSS animations and transitions before the screenshot.",
+          "type": "boolean"
+        },
+        "clock": {
+          "description": "Pause timers and the clock after load on both sides; a page that waits on a timer to render may stay empty.",
+          "type": "boolean"
+        }
+      },
+      "type": "object"
+    },
+    "masks": {
+      "description": "CSS selectors of elements hidden on both sites before the screenshot (at most 50, each up to 200 characters). The box is kept, so the layout does not shift.",
+      "items": {
+        "maxLength": 200,
+        "minLength": 1,
+        "type": "string"
+      },
+      "maxItems": 50,
+      "type": "array"
+    }
+  },
+  "type": "object"
+}

Changed2 schema fields changedOct 11, 2026

addedOutput schema / properties / imageSize

Added value: +{
+  "additionalProperties": false,
+  "properties": {
+    "height": {
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    },
+    "width": {
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    }
+  },
+  "required": [
+    "width",
+    "height"
+  ],
+  "type": "object"
+}

addedOutput schema / properties / region

Added value: +{
+  "additionalProperties": false,
+  "properties": {
+    "height": {
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    },
+    "width": {
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    },
+    "x": {
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    },
+    "y": {
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    }
+  },
+  "required": [
+    "x",
+    "y",
+    "width",
+    "height"
+  ],
+  "type": "object"
+}

Changed4 schema fields changedOct 4, 2026

changedInput schema / properties / idempotencyKey / description

Previous value: -"Optional opaque string a retry repeats: under a prepaid key the same value within 24 hours is not charged again and answers DUPLICATE_REQUEST with the jobId of the first call."New value: +"Optional opaque string a retry repeats: under a prepaid balance the same value within 24 hours is not charged again and answers DUPLICATE_REQUEST with the jobId of the first call."

addedOutput schema / properties / allowanceRemaining

Added value: +{
+  "maximum": 9007199254740991,
+  "minimum": -9007199254740991,
+  "type": "integer"
+}

addedOutput schema / properties / pagesCharged

Added value: +{
+  "maximum": 9007199254740991,
+  "minimum": -9007199254740991,
+  "type": "integer"
+}

addedOutput schema / properties / sample
```
Added value: +{
+  "type": "boolean"
+}
```

Changed1 schema field changedOct 4, 2026

addedInput schema / properties / idempotencyKey

Added value: +{
+  "description": "Optional opaque string a retry repeats: under a prepaid key the same value within 24 hours is not charged again and answers DUPLICATE_REQUEST with the jobId of the first call.",
+  "maxLength": 255,
+  "minLength": 1,
+  "type": "string"
+}

Changed5 schema fields changedOct 2, 2026

removedOutput schema / properties / payment / additionalProperties
```
Removed value: -false
```

addedOutput schema / properties / payment / anyOf

Added value: +[
+  {
+    "additionalProperties": false,
+    "properties": {
+      "amount": {
+        "type": "string"
+      },
+      "balance": {
+        "type": "string"
+      },
+      "currency": {
+        "const": "USD",
+        "type": "string"
+      },
+      "rail": {
+        "const": "prepaid",
+        "type": "string"
+      }
+    },
+    "required": [
+      "amount",
+      "currency",
+      "rail",
+      "balance"
+    ],
+    "type": "object"
+  },
+  {
+    "additionalProperties": false,
+    "properties": {
+      "allowanceRemaining": {
+        "type": "number"
+      },
+      "amount": {
+        "type": "string"
+      },
+      "currency": {
+        "const": "USD",
+        "type": "string"
+      },
+      "pagesFromAllowance": {
+        "type": "number"
+      },
+      "rail": {
+        "const": "subscription",
+        "type": "string"
+      }
+    },
+    "required": [
+      "amount",
+      "currency",
+      "rail",
+      "pagesFromAllowance",
+      "allowanceRemaining"
+    ],
+    "type": "object"
+  }
+]

removedOutput schema / properties / payment / properties

Removed value: -{
-  "amount": {
-    "type": "string"
-  },
-  "balance": {
-    "type": "string"
-  },
-  "currency": {
-    "const": "USD",
-    "type": "string"
-  },
-  "rail": {
-    "const": "prepaid",
-    "type": "string"
-  }
-}

removedOutput schema / properties / payment / required

Removed value: -[
-  "amount",
-  "currency",
-  "rail",
-  "balance"
-]

removedOutput schema / properties / payment / type
```
Removed value: -"object"
```

Changed2 schema fields changedOct 1, 2026
- addedInput schema / properties / auth / properties / password / description
```
Added value: +"Password for HTTP basic auth."
```
- addedInput schema / properties / auth / properties / username / description
```
Added value: +"Username for HTTP basic auth."
```

Changed1 schema field changedSep 29, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": false,
+  "properties": {
+    "bytes": {
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    },
+    "code": {
+      "type": "string"
+    },
+    "dimensions": {
+      "additionalProperties": {},
+      "propertyNames": {
+        "type": "string"
+      },
+      "type": "object"
+    },
+    "error": {
+      "type": "string"
+    },
+    "filename": {
+      "type": "string"
+    },
+    "jobId": {
+      "type": "string"
+    },
+    "jobToken": {
+      "type": "string"
+    },
+    "links": {
+      "additionalProperties": false,
+      "properties": {
+        "file": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "file"
+      ],
+      "type": "object"
+    },
+    "payment": {
+      "additionalProperties": false,
+      "properties": {
+        "amount": {
+          "type": "string"
+        },
+        "balance": {
+          "type": "string"
+        },
+        "currency": {
+          "const": "USD",
+          "type": "string"
+        },
+        "rail": {
+          "const": "prepaid",
+          "type": "string"
+        }
+      },
+      "required": [
+        "amount",
+        "currency",
+        "rail",
+        "balance"
+      ],
+      "type": "object"
+    },
+    "url": {
+      "type": "string"
+    }
+  },
+  "type": "object"
+}

First observedSep 25, 2026

TDQS

A4.6/5.0

Behavior5/5

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

Annotations only declare readOnly=false, openWorld=true, idempotent=false, destructive=false; the description adds genuinely new behavioral facts: a 5-use free quota per client address, no key required, and the delivery split (inline PNG when small, otherwise links.file fetched with the jobToken). The quota and file-fetch mechanics are not derivable from the annotations or the schema, which is exactly the value this dimension rewards.

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

Conciseness4/5

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

Purpose, quota, delivery, and the when-not rule are all front-loaded before the example, which is good ordering. Minor waste: "Call it for a one-off look at a page or a mobile-width check" largely repeats the opening sentence, and the long enumeration of response fields (jobId, jobToken, filename, dimensions, bytes...) duplicates the output schema that already exists.

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?

With an output schema present, annotations supplying the safety profile, and 100% schema coverage, the description only needs to supply what structured data cannot: cost/quota model, no-key auth posture, and where the PNG lands. It supplies all three, plus a concrete invocation example, leaving no practical gap for a correct first call.

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%, so the schema already documents url, auth, visual masks/freeze, viewportWidth, and idempotencyKey in more depth than the description. The description contributes only a mobile context hint for viewportWidth and a sample call with 375; it says nothing about auth, masks, or the retry key. Baseline 3 is the right ceiling when the schema carries the parameter burden.

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

Purpose5/5

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

"Takes a full-page screenshot of one URL" gives a specific verb, resource, and scope in the first clause. It explicitly carves out the boundary against the comparison-job siblings (diff_deploy / wait_for_comparison), so an agent can separate it from every tool in the sibling list without opening a schema.

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

Usage Guidelines5/5

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

It names both the positive case ("a one-off look at a page or a mobile-width check") and the negative case ("Do not call it for pages a comparison job covers: the job already stored their screenshots"), which is an explicit when-not rule tied to a named alternative. Nothing about selection 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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