MCP in Claude Code

Add Onto to Claude Code and Claude Desktop. One config block, one restart.

ℹ

Works with both surfaces. The Claude Code CLI and the Claude Desktop app share the same mcpServers config schema. The only difference is which file you edit.

Install steps

Get an API key

Sign up at app.buildonto.dev/signup. Open /read/keys and copy the live key — it starts with onto_sk_live_. Free tier is 1,000 requests / month, no card required.

Add the server to your MCP config

Paste the block below into the mcpServers object of your Claude config file. If the file or the mcpServers key doesn't exist yet, create them.

jsonclaude_desktop_config.json

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

Or, on Claude Code CLI, run:

bash

claude mcp add onto -- npx -y @ontosdk/mcp@latest
# then set ONTO_API_KEY in the resulting config

Restart fully

Quit the host completely (Cmd+Q / Ctrl+Q, not just close the window) and reopen. MCP servers are loaded once at startup; closing the window does not re-read the config.

Config file location

Claude Desktop:

OS	Path
macOS	~/Library/Application Support/Claude/claude_desktop_config.json
Windows	%APPDATA%\Claude\claude_desktop_config.json
Linux	~/.config/Claude/claude_desktop_config.json

Claude Code CLI: ~/.claude/settings.json — nest the same mcpServers block at the top level.

Verify

After restart, open a new chat and ask:

bash

What MCP tools do I have available?

You should see all six tools — read_url, score_url, read_and_score, batch, map_site, and extract_data — in the list. If they're missing, see Troubleshooting.

Try it

Useful prompts:

◈

"Read https://news.ycombinator.com using Onto and tell me the top three stories."

"Score https://example.com — is it well-structured for AI consumption?"

"Use Onto to read https://stripe.com/pricing and summarize each plan."