Cursor “Connection Failed” and HTTP/2 Errors: Every Fix That Actually Works

“Connection failed. If the problem persists, please check your internet connection or VPN” is one of the most reported Cursor errors, and it is frustrating because it often appears on connections that work everywhere else. The message is generic, so no single fix cures every case. What exists is an ordered set of fixes, each with a different level of evidence: some are in Cursor's documentation, some come from Cursor staff replies on the forum, and some are single-user reports. This guide ranks them honestly and says which is which.

What the error actually means

The message says Cursor could not complete a request to its servers. It does not say why. Reports on the Cursor forum tie it to several different things: HTTP/2 not working well on some networks, too many connected MCP tools, firewall or antivirus interference, VPN or proxy behavior, and in a few cases a stuck chat or corrupted local state. In one thread, users on Linux, macOS, and Windows saw it together with SSLV3_ALERT_HANDSHAKE_FAILURE in the logs, and some said TLS worked from openssl and curl --http2 on the same machine. That points at the path between Cursor's own network stack and its servers, not at the internet being down.

Why HTTP/2 comes up so often

Cursor's documentation states that it uses HTTP/2 for streaming responses and that some corporate proxies, such as Zscaler, block it. HTTP/2 multiplexes many streams over one long-lived connection, so a proxy, VPN, or security tool that mishandles that connection can break streaming while ordinary web browsing still seems fine. Forum staff describe the error as a known issue on some networks with HTTP/2 and recommend the HTTP/1.1 switch first. Two honest caveats: staff have not published a confirmed root cause, and some users report HTTP/2 stopping and starting to work on the same version with no changes, so a version bug is not the whole story either. The same family of problem is covered generally in our guide to debugging streaming failures.

The fix checklist, in order, with evidence

Do the steps one at a time and test in a new chat after each, so you learn which change mattered. If step 2 fixes it, stop; there is no benefit to changing more.

Fixes by situation

If you are on a company network

Ask IT to allow Cursor's domains, and tell them whether TLS inspection is in use. The documented allowlist is *.cursor.sh (including authenticate.cursor.sh and authenticator.cursor.sh), *.cursor-cdn.com, *.cursorapi.com (including marketplace.cursorapi.com), cursor.com and *.cursor.com. Sign-in needs additional hosts listed in Cursor's sign-in domains article, so check the current network documentation, because required hosts change. HTTP/1.1 mode is the quickest workaround while IT sorts out the proxy.

A triage script that gives you the order

The script below turns what you observe into an ordered list of steps, each labeled with its evidence level, so you do not skip the documented ones or present a user report as a guarantee. It also has a helper that returns which of Cursor's hosts you cannot reach, given any probe function you supply. The tests run without Cursor installed.

from dataclasses import dataclass, field

DOCUMENTED, STAFF, USER = "documented", "staff-forum", "user-reported"

CURSOR_HOSTS = ["cursor.com", "authenticate.cursor.sh", "marketplace.cursorapi.com"]


@dataclass
class Observation:
    error_text: str = ""
    http_mode: str = "default"          # "default" or "http1"
    behind_proxy_or_vpn: bool = False
    after_vpn_disconnect: bool = False
    over_ssh: bool = False
    mcp_tool_count: int = 0
    diagnostics_passed: bool = None     # None = not run yet
    fails_only_in_one_chat: bool = False
    failed_hosts: list = field(default_factory=list)


@dataclass
class Step:
    action: str
    evidence: str
    why: str


def triage(o: Observation, mcp_limit: int = 80) -> list:
    steps = []
    if o.diagnostics_passed is None:
        steps.append(Step("Cursor Settings > Network > Run Diagnostics", DOCUMENTED,
                          "Tests the connection to Cursor's servers and flags what breaks AI features."))
    if o.http_mode != "http1":
        why = ("HTTP/2 is used for streaming and some proxies block it."
               if o.behind_proxy_or_vpn else "Staff and users report HTTP/2 problems on some networks.")
        steps.append(Step("Set HTTP Compatibility Mode to HTTP/1.1, then restart Cursor",
                          DOCUMENTED if o.behind_proxy_or_vpn else STAFF, why))
    if o.after_vpn_disconnect:
        steps.append(Step("Fully restart Cursor and confirm system DNS reverted", DOCUMENTED,
                          "Cursor can inherit DNS settings from a previously active VPN."))
    if o.failed_hosts:
        steps.append(Step("Allow these hosts in your firewall: " + ", ".join(sorted(o.failed_hosts)),
                          DOCUMENTED, "Firewalls blocking outbound connections to Cursor's domains break AI features."))
    if o.behind_proxy_or_vpn:
        steps.append(Step("Test without the VPN, proxy, or SSL inspection, or on another network",
                          STAFF, "Isolates whether the network path is the cause."))
    if o.over_ssh:
        steps.append(Step("Check local connectivity and remote CPU and memory; add ServerAliveInterval 60 and ServerAliveCountMax 3",
                          DOCUMENTED, "AI requests leave from your local machine; dropped SSH sessions leave stale processes."))
    if o.mcp_tool_count > mcp_limit * 0.75:
        steps.append(Step(f"Disable unused MCP servers ({o.mcp_tool_count} tools connected)", STAFF,
                          f"A staff reply cites a tool limit of {mcp_limit}; one user fixed the error this way."))
    if o.fails_only_in_one_chat:
        steps.append(Step("Start a new chat; if the problem follows the workspace, back up and clear its chat state as a last resort",
                          USER, "One user traced it to a second agent chat; unconfirmed."))
    if o.diagnostics_passed is False or o.http_mode == "http1":
        steps.append(Step("Collect Request ID, diagnostics output, version, and console errors for support",
                          STAFF, "These are what staff ask for when the usual fixes fail."))
    if "SSLV3_ALERT_HANDSHAKE_FAILURE" in o.error_text:
        steps.append(Step("Note the TLS handshake error in your report", USER,
                          "Reported alongside Connection failed on several operating systems; no root cause confirmed."))
    return steps


def unreachable(probe, hosts=CURSOR_HOSTS) -> list:
    """probe(host) -> bool. Returns the hosts that could not be reached."""
    return [h for h in hosts if not probe(h)]

def acts(steps):
    return [s.action for s in steps]


def test_default_flow_runs_diagnostics_then_http1():
    s = triage(Observation(error_text="Connection failed"))
    assert acts(s)[0].startswith("Cursor Settings > Network > Run Diagnostics")
    assert any("HTTP/1.1" in a for a in acts(s))


def test_proxy_makes_http1_advice_documented_not_forum_only():
    s = triage(Observation(behind_proxy_or_vpn=True, diagnostics_passed=False))
    h = [x for x in s if "HTTP/1.1" in x.action][0]
    assert h.evidence == DOCUMENTED
    plain = [x for x in triage(Observation(diagnostics_passed=False)) if "HTTP/1.1" in x.action][0]
    assert plain.evidence == STAFF


def test_http1_already_set_is_not_repeated_and_escalates():
    s = triage(Observation(http_mode="http1", diagnostics_passed=False))
    assert not any("HTTP/1.1" in a for a in acts(s))
    assert any("Request ID" in a for a in acts(s))


def test_vpn_disconnect_and_ssh_steps():
    s = acts(triage(Observation(after_vpn_disconnect=True, over_ssh=True, diagnostics_passed=True)))
    assert any("DNS" in a for a in s)
    assert any("ServerAliveInterval" in a for a in s)


def test_mcp_advice_only_when_near_the_limit():
    assert not any("MCP" in a for a in acts(triage(Observation(mcp_tool_count=10))))
    s = triage(Observation(mcp_tool_count=70))
    m = [x for x in s if "MCP" in x.action][0]
    assert m.evidence == STAFF and "70 tools" in m.action


def test_failed_hosts_are_listed_sorted_and_single_chat_is_user_reported():
    s = triage(Observation(failed_hosts=["b.cursor.sh", "a.cursor.sh"], fails_only_in_one_chat=True))
    host = [x for x in s if x.action.startswith("Allow")][0]
    assert host.action.endswith("a.cursor.sh, b.cursor.sh")
    chat = [x for x in s if "new chat" in x.action][0]
    assert chat.evidence == USER


def test_unreachable_uses_probe():
    assert unreachable(lambda h: h != "cursor.com") == ["cursor.com"]
    assert unreachable(lambda h: True) == []

What not to do

• Do not reinstall first. One user reported reinstalling as the only fix that worked, but that was a single report and cheaper steps come first.
• Do not delete state before backing up. It removes chat history, and the evidence for it is one user's observation.
• Do not paste Request IDs, console logs, or screenshots publicly without checking them. They can contain workspace paths and account details.
• Do not assume the usage limit is the problem. A staff reply to a user with this error said it is not related to the limit.

If nothing works

Send the information staff ask for: two or three recent Request IDs from Copy Request Details, the Run Diagnostics output, your Cursor version from Help, About, and console errors from Help, Toggle Developer Tools, plus whether a VPN, proxy, or SSL inspection is in the path. For how this error compares with failures in other coding assistants, see Cursor vs Claude Code vs Copilot, and for the same class of problem in Claude Code see Top Claude Code Errors in 2026. If your own code calls model APIs, the broader API error troubleshooting directory covers it.

Sources

• Cursor documentation: Common issues
• Cursor Help: Network troubleshooting
• Cursor forum: Frequent “Connection Failed” errors despite stable internet connection (not official documentation)
• Cursor forum: HTTP/2 makes Cursor unusable (not official documentation)
• Cursor forum: Repeatedly says connection issue when my connection is fine (not official documentation)
• Cursor forum: Always show “connection Error” but usage not to the limit (not official documentation)

Frequently asked questions

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