DiffiCat

Get screenshot

get_screenshot

Read-onlyIdempotent

Fetch one screenshot PNG by filename. Call it when a get_report page result or a capture_screenshot result names a screenshot you want to see; a PNG over the inline cap comes back as links.file to fetch with the jobToken. Pass a report region as region to see only the changed area: regions are in the diff image's coordinates, which share their top-left origin with the source and target screenshots, so one region crops all three. Free.

Input Schema

TableJSON Schema

Name	Required	Description
`jobId`	Yes	The jobId returned when the job was created, e.g. web-1a2b3c.
`region`	No	A region from the report, { x, y, width, height } in screenshot px: only that rectangle is returned, clamped to the image.
`filename`	Yes	A screenshot filename from the report.
`jobToken`	No	The jobToken returned when the job was created. Optional when the request’s HTTP headers carry the key that paid the job.

Output Schema

TableJSON 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
`imageSize`	No
`dimensions`	No
`pagesCharged`	No
`allowanceRemaining`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedOct 11, 2026

addedInput schema / properties / region

Added value: +{
+  "description": "A region from the report, { x, y, width, height } in screenshot px: only that rectangle is returned, clamped to the image.",
+  "properties": {
+    "height": {
+      "description": "Height in px.",
+      "maximum": 4000,
+      "minimum": 1,
+      "type": "integer"
+    },
+    "width": {
+      "description": "Width in px.",
+      "maximum": 20000,
+      "minimum": 1,
+      "type": "integer"
+    },
+    "x": {
+      "description": "Left edge in screenshot px.",
+      "maximum": 9007199254740991,
+      "minimum": 0,
+      "type": "integer"
+    },
+    "y": {
+      "description": "Top edge in screenshot px.",
+      "maximum": 9007199254740991,
+      "minimum": 0,
+      "type": "integer"
+    }
+  },
+  "required": [
+    "x",
+    "y",
+    "width",
+    "height"
+  ],
+  "type": "object"
+}

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 / jobToken / description

Previous value: -"The jobToken returned when the job was created. Optional when the request carries the prepaid key that paid the job (Authorization: Bearer dck_…)."New value: +"The jobToken returned when the job was created. Optional when the request’s HTTP headers carry the key that paid the job."

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"
+}
```

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"
```

Changed1 schema field changedSep 30, 2026
- addedInput schema / properties / jobId / description
```
Added value: +"The jobId returned when the job was created, e.g. web-1a2b3c."
```

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"
+}

Changed2 schema fields changedSep 27, 2026

changedInput schema / properties / jobToken / description

Previous value: -"The jobToken returned when the job was created."New value: +"The jobToken returned when the job was created. Optional when the request carries the prepaid key that paid the job (Authorization: Bearer dck_…)."

changedInput schema / required

Previous value: -[
-  "jobId",
-  "jobToken",
-  "filename"
-]New value: +[
+  "jobId",
+  "filename"
+]

First observedSep 25, 2026

TDQS

A4.6/5.0

Behavior5/5

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

With annotations already declaring read-only/idempotent/non-destructive, the description goes further: it discloses the inline size cap and the links.file + jobToken fallback for oversized PNGs, the coordinate basis of region (diff-image origin shared with source/target), and that the call is Free. That is real behavioral context beyond the structured fields.

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 is front-loaded in the first sentence and every subsequent sentence carries unique information (trigger, oversize fallback, region semantics, cost). The region sentence is dense but earns its place; nothing is wasted.

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 4-param read tool with full schema coverage, annotations, and an output schema, the description fills the remaining gaps an agent needs: when to call, how oversized results are returned, cost, and the coordinate semantics of the only non-obvious optional parameter.

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?

Schema coverage is 100%, so the baseline is 3, but the description adds genuine meaning: it explains that region is expressed in diff-image coordinates that share a top-left origin with the source and target screenshots, so a single region crops all three images. That coordinate-alignment insight is not derivable from the schema alone.

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?

States a specific verb+resource ('Fetch one screenshot PNG by filename') and distinguishes itself from the write-side sibling by naming capture_screenshot as a producer of the filenames it consumes. An agent can tell this is a read of an existing artifact, not a capture.

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?

Gives explicit triggering context: call it when a get_report page result or a capture_screenshot result names a screenshot you want to see. It also explains the region sub-case. It stops short of an explicit 'to create a screenshot use capture_screenshot instead' exclusion, but the context is unambiguous.

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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