Onto MCP Server

The official Onto Model Context Protocol server. Add clean web content reading and AI-readability scoring to Claude Code, Cursor, Cline, Zed, or any MCP-compatible AI client.

What this does

Onto's MCP server exposes these tools to any AI agent:

• read_url — Read any URL and get back clean, agent-ready Markdown (typically 10× smaller than raw HTML)

• score_url — Get the AIO (AI-readability) score for any URL with a breakdown of what helps and what hurts AI consumption

• read_and_score — Both at once: clean content plus quality assessment so the agent knows how much to trust the source

• batch — Read, score, or extract many URLs (an explicit list or a whole site) in one call

• map_site — Discover a site's URLs via its sitemap, without reading them

• extract_data — Return the structured data a page already declares (JSON-LD, OpenGraph, meta)

Every tool response ends with a one-line ⚡ Onto report — reduction, tokens saved, and AIO score — so the value is visible on every call.

This is the official MCP wrapper for the Onto Read API. It's a thin, deterministic layer: Onto cleans and scores with a rule-based engine (no LLM in the loop), so your agent's own model never has to parse raw HTML.

Related MCP server: cleanfetch

Why use this?

When AI agents read websites today, they parse hundreds of KB of React noise to find a few KB of actual content. This burns tokens and causes hallucinations.

Onto strips the noise server-side, returns the agent-ready format, and reports a confidence score for the source. One tool call, one accurate answer.

Quick start

1. Get an Onto API key

Sign up at app.buildonto.dev and create an API key at Read → Keys.

Free tier: 1,000 credits / month. No credit card.

2. Install in Claude Code

Add to your Claude Code MCP config:

{
  "mcpServers": {
    "onto": {
      "command": "npx",
      "args": ["-y", "@ontosdk/mcp@latest"],
      "env": {
        "ONTO_API_KEY": "onto_sk_live_your_key_here"
      }
    }
  }
}

Restart Claude Code. The Onto tools (read_url, score_url, read_and_score, batch, map_site, extract_data) will appear in the available tools list.

3. Install in Cursor

Add the Onto server to ~/.cursor/mcp.json (all projects) or .cursor/mcp.json (this repo). Or use the UI: Customize (sidebar) → MCPs → add a custom server, same JSON.

{
  "mcpServers": {
    "onto": {
      "command": "npx",
      "args": ["-y", "@ontosdk/mcp@latest"],
      "env": {
        "ONTO_API_KEY": "onto_sk_live_your_key_here"
      }
    }
  }
}

Fully quit Cursor (Cmd+Q / Ctrl+Q) and reopen.

See examples/ for Cline, Zed, and Continue configs.

4. Use it

In Claude Code or Cursor, try:

Read https://stripe.com/pricing using Onto and summarize the pricing tiers.

The agent calls read_url, gets clean Markdown, and returns an accurate summary without parsing hundreds of KB of layout HTML.

Tools

read_url

Returns clean Markdown for a URL with metadata about the extraction (sizes, reduction %, cache state).

Input:

score_url

Returns the AIO (AI-readability) score for a URL — 0-100 with a letter grade, hallucination risk, and a structured list of penalties / benefits / recommendations.

Input:

read_and_score

Returns clean Markdown plus the AIO score in one call. Recommended default for agentic workflows.

Input: same as read_url.

batch

Process many URLs in one call. N credits — one per URL in the list after the list is known. Failed URLs (ok: false) are refunded. Default mode read-and-score is still N, not 2N. Give an explicit list or a base URL whose pages are auto-discovered.

Input:

map_site

Discover a site's URLs (sitemap → on-page links) without reading them. 1 credit per call (not per discovered URL) — use it to plan which pages to read or batch next.

Input:

extract_data

Return the structured data a page already declares — JSON-LD, OpenGraph, and meta tags — plus the AIO score. Deterministic; no fields are inferred by a model.

Input:

Pricing

MCP tool credits match the live API meter:

Connect / OAuth is not a debit.

Manage your subscription at app.buildonto.dev/read/billing. Credit packs ($5–$200) are available for overflow once you're on a paid tier.

Configuration

Environment variables:

• ONTO_API_KEY (required) — Your Onto API key from app.buildonto.dev/read/keys

• ONTO_API_BASE (optional) — Override the API base URL (default: https://api.buildonto.dev)

Troubleshooting

"Invalid Onto API key"

Verify your key at app.buildonto.dev/read/keys. If you recently rotated keys, your MCP config may have a stale value.

"Monthly quota exceeded"

You've used your monthly allotment. Upgrade at app.buildonto.dev/read/billing or wait for the monthly reset. Paid tiers can also top up with credit packs.

Tool doesn't appear in Claude Code / Cursor

1. Verify the config file is valid JSON

2. Restart the MCP host (Claude Code, Cursor, etc.)

3. Check the host's MCP logs for connection errors

4. Make sure npx is on your PATH

"Request timed out"

The target site may be slow or unreachable. Onto's request timeout is 15 seconds. Retry, or try a different URL.

Links

• Onto homepage: buildonto.dev

• API documentation: docs.buildonto.dev

• Dashboard: app.buildonto.dev

• GitHub issues: github.com/ravixalgorithm/onto-mcp/issues

• Contact: founder@buildonto.dev

About Onto

Onto is the compatibility layer for the agent web. Three products on one engine:

• Read (this MCP server + API) — AI developers read any URL cleanly

• Serve (Next.js SDK) — Site owners serve clean Markdown to AI crawlers

• Act (coming Q3 2026) — Agents act on websites through semantic intent

Built for AI agents reading the web. Built so they read it correctly.

License

MIT