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HTML/CSS to Image API

by io.github.htmlcsstoimage
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Create an Image of a URL

create_url_image
Destructive

Creates a screenshot of an existing web page at content.url. Rendering loads the page and its resources in a browser and executes its JavaScript. Set content.full_screen for the entire scrollable page, or content.selector to capture a particular element. Returns asset ID, URL, and format information in item; include_image_data requests an eager inline preview. Use create_image when supplying HTML/CSS directly, or create_templated_image when rendering a saved template.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
contentYesPublic HTTP or HTTPS page URL in url, plus optional CSS overrides, viewport, cropping, and loading controls. Set ms_delay when client-side content needs extra time; use render_when_ready only when the page provides the HCTIReadyNow readiness element.
include_image_dataNoEagerly render and include up to 4 MiB of image data for an inline preview. This takes longer and reports progress when the client supports progress notifications. Successful stored renders also return a URL that can be opened or embedded outside the MCP context. Use only when the user requests or needs an inline preview.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
itemNoOperation result. Check success before using this value.
errorNoError details when the operation failed; null on success.
successNoWhether the operation succeeded. If false, inspect error before retrying.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • addedInput schema / properties / content / properties / request_overrides
      Added value: +{
+  "description": "An array of request rules. Use `action: \"block\"` with a `url` wildcard pattern (using `*`) and/or `resource_types` as an array of resource names, such as `image`, `script`, or `xhr`. Both matchers must match when supplied together; any matching block rule blocks the request. Omitted, `null`, or `[]` adds no overrides. Requires a paid plan. Accepts a JSON array in JSON requests or a JSON-encoded array string in form requests. Maximum 100 rules and 512 characters per URL pattern. Each block rule requires a nonempty URL pattern or at least one resource type; supplied matchers cannot be empty. Not supported in query strings.",
+  "items": {
+    "anyOf": [
+      {
+        "properties": {
+          "action": {
+            "const": "block"
+          },
+          "resource_types": {
+            "description": "Resource types to match, supplied as an array of names, such as image, script, xhr, or fetch. Any listed type may match. When url is also supplied, it must match too.",
+            "items": {
+              "enum": [
+                "beacon",
+                "document",
+                "stylesheet",
+                "image",
+                "image_set",
+                "media",
+                "font",
+                "script",
+                "text_track",
+                "xhr",
+                "fetch",
+                "event_source",
+                "manifest",
+                "ping",
+                "img",
+                "other"
+              ],
+              "type": "string"
+            },
+            "type": [
+              "array",
+              "null"
+            ]
+          },
+          "url": {
+            "description": "URL wildcard pattern to match, using * for any sequence of characters. When resource_types is also supplied, both matchers must match.",
+            "type": [
+              "string",
+              "null"
+            ]
+          }
+        }
+      }
+    ],
+    "description": "A browser request override. The action discriminator selects the rule type; currently only block is supported.",
+    "required": [
+      "action"
+    ],
+    "type": "object"
+  },
+  "type": [
+    "array",
+    "null"
+  ]
+}
  2. Changed1 schema field changed
    • changedInput schema / properties / content / properties / disable_twemoji / description
      Previous value: -"Use native Linux emoji rendering instead of HCTI's consistent Twemoji images. Leave `disable_twemoji` unset unless native emoji rendering is specifically needed."New value: +"Set `disable_twemoji: false` explicitly to inject Twemoji into the loaded page. Omitted, `null`, or `true` leaves the page's emoji handling unchanged and does not disable the website's own emoji scripts."
  3. Changed5 schema fields changed
    • changedInput schema / properties / content / description
      Previous value: -"Parameters for creating the image"New value: +"Public HTTP or HTTPS page URL in url, plus optional CSS overrides, viewport, cropping, and loading controls. Set ms_delay when client-side content needs extra time; use render_when_ready only when the page provides the HCTIReadyNow readiness element."
    • changedInput schema / properties / content / properties / url / description
      Previous value: -"The exact public HTTP or HTTPS URL to capture. Use `html` instead when the content can be supplied directly."New value: +"The exact public HTTP or HTTPS URL to capture. Call `create_image` when supplying HTML and CSS directly."
    • addedOutput schema / properties / error / description
      Added value: +"Error details when the operation failed; null on success."
    • addedOutput schema / properties / item / description
      Added value: +"Operation result. Check success before using this value."
    • addedOutput schema / properties / success / description
      Added value: +"Whether the operation succeeded. If false, inspect error before retrying."
  4. First observed

TDQS

A4.4/5.0
Behavior4/5

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

Annotations cover the safety profile (readOnlyHint=false, destructiveHint=true, openWorldHint=true), and the description adds material facts beyond them: rendering loads the page's resources and 'executes its JavaScript', plus that include_image_data triggers an eager inline preview with progress reporting. It does not explain the destructiveHint semantics (stored output) but adds real render-behavior context.

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?

Five tight sentences, front-loaded with purpose, then rendering behavior, key controls, return shape, and sibling routing. No filler; each sentence earns its place.

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

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a complex tool with 100% schema coverage and an output schema, the description is nearly complete: purpose, JS execution behavior, cropping controls, and return fields (asset ID, URL, format via item) are covered. Minor gaps (plan-gated features like proxy/dedupe, the destructiveHint implication) are handled in the schema, so nothing critical is missing.

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 coverage is 100%, so the schema already documents every parameter in depth. The description restates content.full_screen, content.selector, and include_image_data purposes that the schema already establishes, adding little beyond the structured fields. Baseline 3 applies.

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?

Specific verb+resource: 'Creates a screenshot of an existing web page at content.url.' It immediately distinguishes itself from siblings by naming create_image (HTML/CSS directly) and create_templated_image (saved template). An agent can route correctly without opening any 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?

Routes to explicit alternatives with conditions: 'Use create_image when supplying HTML/CSS directly, or create_templated_image when rendering a saved template.' The core 'when' (an existing URL needs capturing) is clear from the first sentence, giving when-to-use plus named alternatives.

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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