Cursor says "Connection failed" and the agent won't answer: every cause and fix

8 min read

Updated: 2d

Last verified: November 13, 2026

You type a request into Cursor's chat or agent panel, the response starts or never starts, and a red banner says the connection failed and suggests checking your internet connection or VPN. Your browser works, other apps work, and yet Cursor keeps refusing. In most cases the request never reaches Cursor's servers at all: something between your computer and Cursor, usually a company proxy, a VPN or a security tool that inspects encrypted traffic, cuts the stream. The fix that solves most cases is switching Cursor's HTTP Compatibility Mode to HTTP/1.1 and fully restarting the app.

Reports on the official Cursor forum come from Windows, macOS and Linux users and go back more than a year, and a wave of new reports followed the 3.9 releases of mid-2026, when Cursor moved its AI features to a separate HTTP/2 connection that some corporate proxies could not handle. Cursor fixed the Windows proxy part of that regression in version 3.11.20, so anyone still on an older 3.9 or 3.10 build should update first and then work through the causes below.

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THE CURSOR "CONNECTION FAILED" MESSAGE AND ITS VARIANTS.

The wording has changed over time, which is why searches for it turn up so many different forum threads. Older builds showed a banner pointing at your network, while builds from mid-2026 onward show a shorter version that suggests trying again. Both come with a Request ID, a code that lets Cursor support find the failed request in its logs. The technical strings in the developer console tell you more about where the connection broke than the banner does.

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Text you see	Where it appears	What it usually points to
Connection failed. If the problem persists, please check your internet connection or VPN	Chat or agent panel, older builds	Network path to Cursor blocked or interrupted
Connection failed. Please try again, or contact support if the issue persists.	Chat or agent panel, 2026 builds	Same, request did not reach Cursor's servers
ConnectError: [unavailable]	Developer Tools console	Streaming connection dropped, often by a proxy
RetriableError: [unknown] Network disconnected	Developer Tools console	Connection cut mid-stream
ERR_NAME_RESOLUTION_FAILED or getaddrinfo EAI_AGAIN api2.cursor.sh	Console and logs	DNS could not resolve Cursor's API host
Suspicious activity	Chat panel	Request blocked as a security measure, a VPN can trigger it

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Cursor staff have described the 2026 banner as a retriable error: resending the same message often works, which tells you Cursor's servers are healthy and the problem sits on the network path. If resending works once and then fails again a few minutes later, the cause is usually one of the network conditions in the next section.

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WHY CURSOR LOSES THE CONNECTION: CAUSES, CHECKS AND FIXES.

Cursor streams model responses over HTTP/2, a newer version of the web protocol that keeps one connection open and sends the answer in pieces. Some corporate proxies and security gateways block HTTP/2 or hold the stream until it times out, and Cursor's documentation names that as the first thing to fix. It accounts for a large share of the reports answered by staff, while DNS problems left by a VPN, local proxy apps, firewalls and stuck sessions account for the rest.

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Cause	How to check	Fix
Corporate proxy or SSL inspection blocks HTTP/2 (Zscaler, Palo Alto and similar)	Run Diagnostics in Cursor Settings > Network shows failed Chat or Agent checks	Set HTTP Compatibility Mode to HTTP/1.1, then quit and relaunch
Cursor 3.9.x ignoring the Windows system proxy	Help > About shows a 3.9 or 3.10 build and you are behind a proxy	Update to 3.11.20 or later
VPN changed DNS and Cursor kept the old settings	Errors mention name resolution or api2.cursor.sh	Fully restart Cursor; check system DNS has reverted
Firewall or allowlist missing Cursor domains	IT confirms traffic to cursor.sh or cursorapi.com is blocked	Allowlist the domains listed below
Local proxy app or slow route adds high latency	Diagnostics Ping takes more than a second	Remove 127.0.0.1 proxy entries, turn off TUN mode, use a faster route
Stuck agent session, extensions or MCP servers	Error repeats in one chat but not in a new one	Start a new chat; test with extensions and MCP servers turned off
Cursor service incident	status.cursor.com lists an active incident	Wait for the incident to be resolved

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Running the built-in diagnostics first saves time, because it tells you whether DNS, SSL, the chat stream or the agent stream is the part that fails.

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STEP-BY-STEP FIXES FOR CURSOR CONNECTION ERRORS.

Start with the diagnostics and the compatibility switch, since together they resolve the majority of cases, then move down the list only if the error persists.

1. Open Cursor Settings, go to the Network section and click Run Diagnostics. Note which checks fail: DNS, SSL, Ping, Chat or Agent. A screenshot of this result is also the first thing Cursor support asks for.

2. In the same Network section, set HTTP Compatibility Mode to HTTP/1.1. Cursor's documentation names this as the fix for proxies such as Zscaler that block HTTP/2. Staff say it costs a little latency and fixes most cases.

3. Quit Cursor completely and open it again. Reload Window keeps the old network state, so use Quit (Cmd+Q on macOS) or close every window on Windows and Linux. Cursor staff repeat this point in their forum replies, because a reload leaves the broken connection in place.

4. Check your version under Cursor > About Cursor on macOS or Help > About on Windows and Linux. If it is a 3.9 or 3.10 build, update. Cursor staff confirmed that the regression in which the new HTTP/2 transport bypassed the Windows system proxy was fixed starting in version 3.11.20.

5. Turn off your VPN temporarily and send a new message. If Cursor works without it, the VPN route or its DNS is the problem. After disconnecting a VPN, fully restart Cursor, since the app can keep the DNS settings the VPN pushed.

6. Start a new agent chat. Staff note that the error sometimes stays attached to a single session, and a fresh chat clears it.

7. Rule out extensions and MCP servers. Launch Cursor from a terminal with the command shown below, which starts it with every extension turned off, and switch off MCP servers you are not using in the MCP section of Cursor Settings. MCP servers are external tools the agent can call; staff have suggested disabling unused ones when the error appears during agent runs.

8. Check status.cursor.com. If an incident is listed, no local change will help until Cursor resolves it.

cursor --disable-extensions

If none of these steps work, copy the Request ID from the "..." menu of the failed response (Copy Request ID) and post it on forum.cursor.com together with the diagnostics screenshot, your Cursor version and operating system, and any errors from Help > Toggle Developer Tools > Console. Cursor's documentation says connectivity problems can usually be investigated with Privacy Mode left on.

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CURSOR BEHIND A CORPORATE PROXY OR SSL INSPECTION.

Company networks cause the most stubborn cases, because the proxy decides what passes and you may not control it. When HTTP Compatibility Mode alone does not help, Cursor staff have given developers a set of manual settings to force HTTP/1.1 and route Cursor through the proxy explicitly. They go in Cursor's settings.json (open the Command Palette and choose the option to open user settings as JSON). The block below reproduces the settings named by Cursor staff on the official forum; replace the address with your company's proxy.

"cursor.general.disableHttp2": true,
"http.proxy": "http://proxy.example.com:8080",
"http.proxySupport": "override"

Staff added that `"http.proxyStrictSSL": false` can help when the proxy inspects encrypted traffic, but that setting stops Cursor from checking the proxy's certificate, so use it only on a network your IT team manages and remove it once the proxy is configured properly. On Windows, staff also suggested starting Cursor once with `Cursor.exe --no-proxy-server` to rule out a cached system proxy.

The lasting fix belongs to IT. Cursor's network documentation lists the domains that must be allowed through firewalls and excluded from TLS inspection.

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Domain	Used for
*.cursor.sh	API and sign-in (authenticate.cursor.sh, authenticator.cursor.sh)
*.cursorapi.com	Services and extension marketplace
*.cursor-cdn.com	Downloads and static content
cursor.com and *.cursor.com	Web dashboard, Cloud Agents web interface, code review
.cursorvm.com and .*.cursorvm.com	Hosted computer used by Grok Bot

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Cursor also documents a related symptom on the web: Cloud Agents stuck on "Loading…" at cursor.com when a secure web gateway such as Cloudflare WARP, Zscaler or Netskope scans the page and holds the stream. Opening cursor.com/agents from a network without the gateway confirms it, and the fix is the same exclusion from TLS inspection. If the diagnostics report that "HTTP/1.1 SSE responses are being buffered by a proxy", a staff member explained in October 2026 that the check fails whenever the first streamed response takes longer than two seconds, so a slow network route can trigger the same warning.

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CURSOR CONNECTION FIXES ON WINDOWS, MACOS AND LINUX.

Most steps are identical across systems, but a few checks depend on the platform.

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Platform	Specific check	Source
Windows	Update past the 3.9.x proxy regression (fixed in 3.11.20); try Cursor.exe --no-proxy-server once	Cursor staff, official forum
Windows (managed PCs)	Ask IT to add exclusions for Cursor in endpoint security software	Cursor documentation
macOS	Run scutil --dns to confirm DNS reverted after a VPN; remove proxy entries pointing to 127.0.0.1 in network settings	Cursor documentation and staff
Linux	Check /etc/resolv.conf for a leftover VPN resolver	Cursor documentation
Remote SSH	Check the local connection first, since AI requests leave from your own machine	Cursor documentation

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On macOS, developers who run a local proxy app often leave it in TUN or "enhanced" mode, which captures all traffic. A Cursor staff member identified this from a diagnostics screenshot in which the SSL check pointed at 127.0.0.1, and recommended turning that mode off or switching to a faster route until the Ping check stays well under one second.

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WHAT CURSOR DOCUMENTS AND WHAT COMES FROM FORUM REPORTS.

Cursor's help pages document the diagnostics tool, the HTTP Compatibility Mode switch, the allowlist of domains, the VPN and DNS advice, the Request ID and the status page. The Windows proxy regression, its fix in 3.11.20, the settings.json values, the --no-proxy-server flag, the advice about extensions and MCP servers and the latency explanation of the buffering warning come from replies by Cursor staff on the official forum. Users there have also reported that some corporate proxies keep failing even on HTTP/1.1; staff answered that in those setups the proxy itself is cutting or buffering the traffic, and only an IT-side exclusion solves it. Cursor has not published a single page that maps each variant of the banner to a cause.

If you work on your own machine without a VPN or proxy and the error still appears, the earlier coding-tool connection issues covered in our page on Codex reconnecting and "stream disconnected before completion" follow the same pattern: an interrupted stream, a retry, and a network path that drops long responses.

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KEEPING CURSOR CONNECTED AFTER UPDATES.

Network behaviour in Cursor can change with a release, as the 3.9 transport change showed. After a major update, run Network Diagnostics once, especially on a company network, and keep the compatibility mode on HTTP/1.1 if your network needs it. If you had pinned an older version or turned off automatic updates as a workaround during the 3.9 period, Cursor staff advised re-enabling updates and removing the workaround settings once you are on 3.11.20 or later.

Starting a new chat is one of the quickest fixes when a single session keeps failing, and forum reports show the error often appearing during agent runs that build or test code. Moving to a fresh chat is easier when your instructions live in project rules instead of the conversation, and our page on why Cursor project rules are not applied explains how to make them load reliably in every new chat. For an overview of how the editor and its agent work, see our guide to Cursor Composer 2, its pricing and where it fits.

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CURSOR "CONNECTION FAILED": WHAT TO DO FIRST.

The banner points at your internet connection, yet in most reports the connection works and Cursor's streaming request is the part that does not survive the path to its servers, cut by a proxy, a VPN or an inspection tool. Running Network Diagnostics, switching HTTP Compatibility Mode to HTTP/1.1 and fully restarting the app resolves the majority of cases, and updating to 3.11.20 or later removes the Windows proxy bug of the 3.9 releases. When a company network still blocks the stream, the domains Cursor publishes for allowlisting and TLS-inspection exclusions are what IT needs, and a Request ID with a diagnostics screenshot is what Cursor support needs to trace a failure that persists.

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DATA STUDIOS

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