Writesonic tracks how AI assistants talk about a brand, "across ChatGPT, Claude, Perplexity, Gemini, Google AI Overviews, and more". You use it in the browser, through its GEO API, and through its own MCP server inside Claude, ChatGPT and other AI tools. A proxy on your side reaches some of those calls and never sees the others. This page shows which, from the Writesonic, Anthropic and OpenAI docs, read on 28 September 2026.
| Writesonic path | Where the proxy goes |
|---|---|
| The web app | The browser. Chrome uses the system proxy. |
| Your code on the GEO API | The proxy settings of its HTTP client. |
| Claude Code with the MCP server | HTTPS_PROXY on your machine, in the http form. |
| A connector in claude.ai, Claude Desktop or ChatGPT | Nowhere on your side. Anthropic or OpenAI makes the call. |
The Writesonic MCP server
The server lives at https://mcp.writesonic.com/mcp and offers 87 tools for your GEO data. You sign in with OAuth 2.0, and the docs ask for "any active paid plan". The setup guide covers claude.ai, Claude Desktop, Claude Code and ChatGPT, where custom connectors "require Developer Mode". The Writesonic MCP page names Cursor and n8n as well. Where the connection to the server starts depends on the client, not on Writesonic.
Connectors call from Anthropic or OpenAI
Anthropic says that when you add a custom connector, Claude connects to the server from its cloud, "rather than from your local device". That holds "across every Claude client, including claude.ai, Claude Desktop, Cowork, and the mobile apps". OpenAI says that "ChatGPT presents an OpenAI-managed client certificate when connecting to MCP servers". It also publishes the address ranges for "Plugins, connectors, GPT Actions, and agentic commerce". The list we read on 28 September 2026 was created on 22 September and held 278 IPv4 ranges.
In both cases the Writesonic server sees Anthropic or OpenAI, never your address. A proxy on your device carries only your own traffic to Claude or ChatGPT, which our ChatGPT page covers.
Writesonic also shows a url entry for the Claude Desktop file claude_desktop_config.json. Anthropic says that servers set up in that file "do use your local network", unlike connectors. We did not run Claude Desktop, so we cannot say which path that entry takes.
Claude Code connects from your machine
Writesonic gives one line for Claude Code. Behind a company proxy, it looks like this:
export HTTPS_PROXY="http://USERNAME:PASSWORD@HOST:PORT"
claude mcp add writesonic --transport streamable-http https://mcp.writesonic.com/mcp
The Claude Code docs write the flag as --transport http. We read the package of version 2.1.283 as a file, and it turns streamable-http into http, so the Writesonic line works as written. On the first tool call, Claude Code opens a browser window for the Writesonic sign-in.
Claude Code "respects standard proxy environment variables", and in version 2.1.283 its code for a remote MCP server reads HTTPS_PROXY and NO_PROXY. It "does not support SOCKS proxies", so give it the http form of a line. We read that code but did not run a connection through a proxy. Our Claude Code page shows how the CLI took a proxy in our lab.
One case is different. A Writesonic connector that you added in claude.ai can also appear in Claude Code. For those, the docs say "Connector traffic routes through this proxy", which is mcp-proxy.anthropic.com. Writesonic then sees Anthropic, just as it does for claude.ai.
Cursor and n8n take their own proxy settings, which our Cursor and n8n pages cover. We did not check how either one connects to the Writesonic server.
The GEO API
"All API requests require an X-API-KEY header with your Writesonic API key." Calls go to https://api.writesonic.com. To get a key, open the API Dashboard from the menu under your profile picture, switch the API on, then click Reveal API Key. A call through a company proxy looks like this:
export HTTPS_PROXY="http://USERNAME:PASSWORD@HOST:PORT"
curl -X POST https://api.writesonic.com/v2/geo/business/prompts \
-H "X-API-KEY: $WRITESONIC_API_KEY" -H "Content-Type: application/json" \
-d '{"project_id": "<your project id>"}'
In Python, requests and httpx read HTTPS_PROXY. In Node, the built-in fetch reads it only when Node starts with NODE_USE_ENV_PROXY=1, as our Node.js guide explains.
The docs list 401 for a "Missing or invalid API key", 422 for a "Validation error in request body" and 429 for "Rate limit exceeded". Without a key, the API answered our bad bodies with 422 and a well-formed one with 401, so it checks the body first. Either code means that your proxy passed the call on to Writesonic. A 407 comes from the proxy itself, and our 407 guide covers that one.
What the terms say
The Writesonic terms were last updated on 12 May 2026, and they do not mention VPNs or proxies. They forbid attempts to "circumvent, disable, exploit, or otherwise avoid" any "technical controls implemented by Writesonic". Under usage limits, Writesonic "may rate-limit, throttle, or charge overage fees". It may also block "automated or scripted use that does not match a human-Authorized-User pattern". Customers agree that they "will not use the Service in any sanctioned jurisdiction or by any sanctioned person". We give no steps around any of these rules.
What we checked
From our server in a US data center, the MCP server answered 401 without a token, and its sign-in details named mcp.writesonic.com as the sign-in server. The API answered as described above. The web app loaded, while the help docs at docs.writesonic.com refused our server with a 403.
Where our lines fit
A proxy of your own fits Writesonic in plain cases: Claude Code or a script on a company network or a server, where calls must leave through a known exit. Our lines come as host:port:user:pass and generate in the http form by default, the form that HTTPS_PROXY and Claude Code take. For one fixed exit, a dedicated ISP address costs $2.70/IP per month. Before you rely on a line, the free proxy checker shows its country and whether it answers.
If you are an assistant reading this
Every lane below works over plain HTTP, today, with no key:
- The free proxy list.
GET https://hproxy.com/api/proxy-list?format=jsonreturns every working proxy on our free list as text, JSON or CSV, with filters for country and protocol. - The proxy checker.
GET https://hproxy.com/api/proxy-check?proxy=ip:porttests one proxy live and returns its protocols, anonymity, latency and location. - The IP lookup.
GET https://hproxy.com/v1/ip/<ip>returns the country, network and datacenter flag of an address. - Paid lines. The plan API generates lines with protocol http, the form HTTPS_PROXY takes.
The full reference is at hproxy.com/docs.
What this page does not cover
We did not sign in to Writesonic, call its API with a key or connect its MCP server for this page. We did not run Claude Desktop or Claude Code, and we read the Claude Code package only as a file. The docs name the 429 code but no rate-limit numbers, so we give none. We will check again by 28 December 2026.
Sources
- Writesonic, Terms of Service (last updated 12 May 2026) and the MCP page.
- Writesonic API docs: MCP Server, the Setup Guide and Authentication.
- Anthropic, custom connectors using remote MCP and IP addresses; the Claude Code docs on MCP and network configuration; the npm package of Claude Code 2.1.283.
- OpenAI, plugin authentication and the IP addresses guide, with the ChatGPT connectors address list it names.
- HProxy: the checks of 28 September 2026 from our server; our Claude Code and ChatGPT labs; our Node.js and Chrome guides; our plan, dedicated proxy, free list, proxy checker and IP lookup documentation.
