# web.dev API: Check page speed

> Tests a web page with Google PageSpeed Insights on mobile or desktop: performance, accessibility, best practices and SEO scores, lab timings, real-user Core Web Vitals when available, and the top suggested fixes.

Unofficial. Not affiliated with or endorsed by web.dev.

- Page: https://fous.com/methods/pagespeed.web.dev/check-page-speed
- Method: `pagespeed.web.dev/check_page_speed`, version 1
- Website: pagespeed.web.dev
- Returns: scores, lab results, real-user results, suggested fixes, tested link, report link
- Effect: read (it gets data and changes nothing)
- Sign-in: none needed
- Cost: 1 credit per completed run (1¢ with pay as you go); failed runs are free
- Verified: Nov 2, 2026

## Inputs

| Field | Type | Required | In the run below | Description |
|---|---|---|---|---|
| `device` | string | no | `"desktop"` | Device type, such as mobile. One of "mobile", "desktop". Default "mobile". |
| `page_url` | string | yes | `"example.org"` | Address of the page to test, such as example.com. |

## Output

From a run on Oct 31, 2026, shortened. Its input:

```json
{
  "device": "desktop",
  "page_url": "example.org"
}
```

Its output:

```json
{
  "device": "desktop",
  "seo_score": 80,
  "lab_results": {
    "speed_index_seconds": 0.206,
    "total_blocking_time_ms": 0,
    "first_contentful_paint_seconds": 0.206,
    "largest_contentful_paint_seconds": 0.206
  },
  "report_link": "https://pagespeed.web.dev/analysis/https-example-org/3qxczoum24?form_factor=desktop",
  "tested_link": "https://example.org/",
  "suggested_fixes": [
    {
      "fix": "Use efficient cache lifetimes",
      "estimated_saving": "Est savings of 1 KiB"
    },
    {
      "fix": "Forced reflow",
      "estimated_saving": null
    },
    {
      "fix": "Network dependency tree",
      "estimated_saving": null
    }
  ],
  "performance_score": 100,
  "real_user_results": {
    "scope": "URL",
    "passed": true,
    "cumulative_layout_shift": 0,
    "interaction_to_next_paint_ms": 15,
    "largest_contentful_paint_seconds": 0.579
  },
  "accessibility_score": 96,
  "best_practices_score": 100
}
```

## Run it

From code, with a Fous API key in `FOUS_API_KEY`; the answer's `data` holds the output:

```bash
curl https://api.fous.com/v1/runs \
  -H "Authorization: Bearer $FOUS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"method":"pagespeed.web.dev/check_page_speed","input":{"device":"desktop","page_url":"example.org"}}'
```

From an AI agent connected to the Fous MCP server: its `run` with the same method and input. To connect one, give it `set up https://fous.com/SKILL.md`.

## Ask your agent

- Run a PageSpeed Insights test on https://www.etsy.com/c/jewelry for mobile and tell me the performance and accessibility scores
- How fast does bluebottlecoffee.com load on desktop? I want the LCP, CLS and the biggest fixes to make it quicker
- Use web.dev to check the Core Web Vitals for my portfolio site janedoe.design on a phone
- Can you audit nytimes.com/section/technology on web.dev for desktop and give me the SEO and best practices scores plus a link to the full report?
- Our landing page at shop.greenleafgardens.co.uk feels sluggish on mobile — test it and list the top suggested improvements along with real-user data if there is any

## Input schema

```json
{
  "type": "object",
  "required": [
    "page_url"
  ],
  "properties": {
    "device": {
      "enum": [
        "mobile",
        "desktop"
      ],
      "type": "string",
      "default": "mobile",
      "description": "Device type, such as mobile."
    },
    "page_url": {
      "type": "string",
      "description": "Address of the page to test, such as example.com."
    }
  }
}
```

## Output schema

```json
{
  "type": "object",
  "required": [
    "tested_link",
    "device",
    "performance_score",
    "accessibility_score",
    "best_practices_score",
    "seo_score",
    "real_user_results",
    "lab_results",
    "suggested_fixes",
    "report_link"
  ],
  "properties": {
    "device": {
      "type": "string",
      "description": "Device type tested."
    },
    "seo_score": {
      "type": [
        "number",
        "null"
      ],
      "description": "SEO score out of 100."
    },
    "lab_results": {
      "type": "object",
      "properties": {
        "speed_index_seconds": {
          "type": [
            "number",
            "null"
          ],
          "description": "Lab speed index in seconds."
        },
        "total_blocking_time_ms": {
          "type": [
            "number",
            "null"
          ],
          "description": "Lab total blocking time in milliseconds."
        },
        "first_contentful_paint_seconds": {
          "type": [
            "number",
            "null"
          ],
          "description": "Lab first contentful paint in seconds."
        },
        "largest_contentful_paint_seconds": {
          "type": [
            "number",
            "null"
          ],
          "description": "Lab largest contentful paint in seconds."
        }
      },
      "description": "Results measured by Lighthouse."
    },
    "report_link": {
      "type": "string",
      "description": "Link to the full PageSpeed Insights report."
    },
    "tested_link": {
      "type": "string",
      "description": "Final page address tested."
    },
    "suggested_fixes": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "fix": {
            "type": "string",
            "description": "Suggested improvement."
          },
          "estimated_saving": {
            "type": [
              "string",
              "null"
            ],
            "description": "Estimated saving shown by PageSpeed, if any."
          }
        }
      },
      "description": "Up to five relevant suggested fixes."
    },
    "performance_score": {
      "type": [
        "number",
        "null"
      ],
      "description": "Performance score out of 100."
    },
    "real_user_results": {
      "type": [
        "object",
        "null"
      ],
      "properties": {
        "scope": {
          "type": "string",
          "description": "Whether data describes the URL or its origin."
        },
        "passed": {
          "type": [
            "boolean",
            "null"
          ],
          "description": "Whether Core Web Vitals passed."
        },
        "cumulative_layout_shift": {
          "type": [
            "number",
            "null"
          ],
          "description": "Real-user cumulative layout shift."
        },
        "interaction_to_next_paint_ms": {
          "type": [
            "number",
            "null"
          ],
          "description": "Real-user interaction to next paint in milliseconds."
        },
        "largest_contentful_paint_seconds": {
          "type": [
            "number",
            "null"
          ],
          "description": "Real-user largest contentful paint in seconds."
        }
      },
      "description": "Real-user experience when available."
    },
    "accessibility_score": {
      "type": [
        "number",
        "null"
      ],
      "description": "Accessibility score out of 100."
    },
    "best_practices_score": {
      "type": [
        "number",
        "null"
      ],
      "description": "Best practices score out of 100."
    }
  }
}
```

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