@agent-sh/harness-web-mcp

MCP server that gives Claude Code, Codex, and any other MCP client two web tools:

• websearch: web search with no API key and no setup (Exa → Parallel → Mojeek → Marginalia → Wikipedia). Add Brave, Tavily or a self-hosted SearXNG for more coverage.
• webfetch: fetch a URL and get clean markdown back, with SSRF defense, redirect reporting, size caps and a per-session cache.

They are the @agent-sh/harness-websearch and @agent-sh/harness-webfetch tools served over stdio, with their own descriptions and schemas unchanged. Part of the agent-sh/tools monorepo.

Add it to your agent

Claude Code

claude mcp add -s user harness-web -- npx -y @agent-sh/harness-web-mcp

Codex

codex mcp add harness-web -- npx -y @agent-sh/harness-web-mcp

Restart the agent (in Claude Code, /mcp reconnects). The tools show up as mcp__harness-web__websearch and mcp__harness-web__webfetch in Claude Code, and as harness-web tools in Codex.

npx -y downloads the latest version on first start. To pin a version, or skip npx's startup cost, install it globally and point the client at the binary:

npm i -g @agent-sh/harness-web-mcp
claude mcp add -s user harness-web -- harness-web-mcp

Claude Code (~/.claude.json, or a project .mcp.json):

{
  "mcpServers": {
    "harness-web": {
      "command": "npx",
      "args": ["-y", "@agent-sh/harness-web-mcp"],
      "env": { "BRAVE_API_KEY": "optional" }
    }
  }
}

Codex (~/.codex/config.toml):

[mcp_servers.harness-web]
command = "npx"
args = ["-y", "@agent-sh/harness-web-mcp"]

[mcp_servers.harness-web.env]
BRAVE_API_KEY = "optional"

Any other MCP client: run npx -y @agent-sh/harness-web-mcp as a stdio server.

Configuration

Everything is optional; with no configuration you get keyless search and strict fetch.

| Variable | Effect | |---|---| | BRAVE_API_KEY | Brave leads the search chain; the keyless chain remains a fallback. Free tier at api-dashboard.search.brave.com. | | TAVILY_API_KEY | Tavily joins the head of the search chain. | | EXA_API_KEY, PARALLEL_API_KEY | Raise those engines' keyless rate limits. | | SEARXNG_URL | Self-hosted SearXNG (e.g. http://127.0.0.1:8888) leads the chain. Loopback is allowed for this URL only. | | HARNESS_WEB_FETCH_ALLOW_LOOPBACK=1 | Let webfetch reach localhost. Off by default. | | HARNESS_WEB_FETCH_ALLOW_PRIVATE=1 | Let webfetch reach private networks (RFC 1918). Off by default. |

Pass variables with claude mcp add -e KEY=value …, codex mcp add --env KEY=value …, or the env block in the config file.

Safety

• The MCP client approves each call. Claude Code and Codex ask before running a tool unless you allow it, so this server does not add a second permission prompt.
• webfetch refuses loopback, private networks and cloud metadata endpoints by default, resolves DNS once to block rebinding, and caps response size.
• Treat results as data, not instructions. Both tool descriptions tell the model so, because a fetched page or a search snippet can contain prompt-injection text.
• Search queries go to the engines in the chain (Exa, Parallel, Mojeek, Marginalia, Wikipedia, plus any keyed engine you add).

Programmatic use

import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import { createWebMcpServer, optionsFromEnv } from "@agent-sh/harness-web-mcp";

await createWebMcpServer({ ...optionsFromEnv(), braveApiKey: process.env.MY_KEY })
  .connect(new StdioServerTransport());

License

MIT © Avi Fenesh