Cursor MCP Down? Route GitHub and SSE Hosts in Clash (2026)

1. Why MCP failures look like “everything is broken”

Most frustrated screenshots share the same caption: “I added MCP and it just spins.” Behind that single sentence are at least three different planes. The first plane is editor chrome: signing in, loading the Marketplace, downloading VSIX-style assets, and hydrating extension CDNs. The second plane is inline model traffic: completion APIs, billing surfaces, and telemetry hosts that resemble other assistants we have covered elsewhere. The third plane—and the one this article targets—is MCP transport: resolving where a server lives, fetching install instructions or packaged binaries (often from GitHub), negotiating OAuth or API tokens against a vendor control cluster, opening the primary HTTPS session, and finally keeping an SSE channel open long enough for incremental tool output to arrive.

When users conflate those planes, they apply the wrong fix. Tightening Marketplace rules does nothing if the MCP binary never finishes downloading from objects.githubusercontent.com. Raising global tunnel bandwidth does nothing if DNS and fake-ip disagree about what the SSE hostname resolves to, because the client will keep retrying TLS handshake steps that never line up with the policy that owns the underlying TCP flow. The practical habit is to reproduce the failure once with logging enabled, then tag each hostname you see into a bucket before you touch YAML.

If your subscription still feels opaque, skim our subscription import tutorial so you know where provider rules end and your personal exception list begins. Everything below assumes you can append suffix rules without breaking schema validation.

2. Symptoms that separate TLS/DNS issues from “slow nodes”

Before you chase latency leaderboards, classify the failure by time and protocol shape. Classic TLS handshake friction shows up quickly: the MCP panel advances to “connecting,” then stalls before any tool list renders, often paired with certificate or reset errors in developer tooling if you enable verbose logs. That pattern frequently correlates with Mihomo rows where the same logical vendor alternates between PROXY and DIRECT across closely related hostnames, or where the first hop uses a domestic resolver answer while the second hop expects a different geography.

SSE failures look different. The first HTTPS request may succeed—your server metadata appears—but streaming lines never increment, or they freeze after the first partial payload. Because SSE is a long-lived HTTP response, mid-flight proxy failovers, idle timeouts on cheap intermediates, or accidental double-NAT through stacked VPN products show up as “random disconnects” rather than instant hard errors. Users describe that as “Cursor MCP is flaky,” yet the root cause is session stability, not average Mbps.

Spinner-only cases with no UI error often map to GitHub asset paths. The editor may be waiting on a release download while the visible UI thread still looks idle. When you sort Mihomo connections during reproduction, watch for github.com, api.github.com, raw.githubusercontent.com, and objects.githubusercontent.com in the same minute as your MCP attempt. If those rows never appear in Clash at all, you still have a visibility problem—system proxy bypass or a child process that does not inherit the tunnel—before you have a rule-depth problem.

3. Anatomy of a remote MCP stack in 2026

Remote MCP servers are not a single hostname. Discovery may reference a registry document, a vendor-specific API catalog, or a pinned JSON manifest hosted on GitHub. Package distribution still leans heavily on GitHub proxy paths for small teams: release archives, checksum files, and README deep links. Enterprise deployments may add an internal mirror, but the debugging mindset stays the same: enumerate every hostname the client touched between “add server” and “first successful tool call.”

The control plane for HTTP-based MCP is ordinary HTTPS with modern TLS. The streaming plane is still HTTPS, yet semantics resemble lightweight long polling: the server holds the response open, pushes discrete data: lines, and expects the client parser to remain attached. Any middlebox that buffers aggressively, inspects half of the bytes, or rewrites chunked encodings can break SSE without triggering the same symptoms on short REST calls.

Finally, remember that AI toolchain traffic is multi-tenant. A profile tuned for one assistant’s API endpoints may silently mis-route another vendor’s SSE cluster if both share a broad CDN pattern that your subscription labels “domestic direct.” That is why hostname-level Clash split routing beats blunt GEO rules when MCP is on the critical path.

4. Triage order: visibility, DNS, rules, then session stability

Rotate exit nodes only after cheaper checks fail. Work through this sequence while keeping your client’s live connection view open so you can read the policy column per hostname.

1. Confirm whether Cursor’s helper processes inherit your Clash mode: system proxy versus TUN. Endpoint security products sometimes strip OS proxy flags for selected binaries.
2. Reproduce the MCP stall, then read Mihomo logs for the exact minute. Stray DIRECT rows next to proxied GitHub hosts are a common smoking gun for partial downloads.
3. Audit DNS: upstream reachability, fake-ip expectations, and whether campus resolvers special-case GitHub or AI vendor domains.
4. Expand explicit GitHub proxy coverage beyond the apex domain to include API, raw, and object hosts observed in your capture.
5. Add vendor SSE edges and OAuth-adjacent APIs as a coherent bundle on one stable policy group, then reduce hyperactive auto failover for those destinations.

For port collisions, invalid rules, and core startup failures, keep the general Clash troubleshooting guide open. Here we focus on IDE-adjacent MCP transports where one missing suffix mimics a total outage.

5. GitHub is several traffic classes, not one domain

Teams routinely paste DOMAIN-SUFFIX,github.com,PROXY and assume the job is done. Real captures almost always include sibling names. REST metadata often flows through api.github.com. Small text assets use raw.githubusercontent.com. Large release artifacts frequently land on objects.githubusercontent.com or other CDN-shaped hosts that share little with the apex string match. If any of those classes take a different policy than the others, you can observe bizarre partial progress: authentication succeeds, yet the packaged MCP binary never lands, leaving the UI thread waiting forever.

Another subtle failure is HTTP/3 or QUIC experimentation. Some networks block UDP-based transports while leaving TCP 443 untouched. If your log shows QUIC attempts failing while TCP fallback never triggers because the client pinned the wrong path, temporarily aligning the relevant hosts to a TCP-friendly exit can unblock MCP setup even though “the website still loads in a browser.” Document what you changed; QUIC defaults shift across releases.

For a broader Microsoft plus GitHub mental model—useful when Copilot traffic mingles with MCP downloads—see our GitHub Copilot and Microsoft CDN split article. The hostname vocabulary differs, yet the discipline of reading sibling rows in Mihomo transfers directly.

6. Domain buckets you can defend in a change request

Static rule posts decay because CDNs and feature flags shift. Treat the table as a hypothesis checklist; verify suffixes against your own logs before you paste.

When you document fixes for IT, paste the hostname list with a capture date. Future you will appreciate the timestamp when a vendor migrates SSE edges to a new certificate name.

7. DNS, fake-ip, and why MCP hates inconsistency

Clash’s fake-ip mode answers quickly with synthetic addresses, yet it tightly couples DNS to rule evaluation. When the resolver and the rule engine disagree about what a hostname “means,” you can observe TLS handshake retries, stalled MCP panels, or streams that open then immediately reset. MCP amplifies the pain because setup often bursts dozens of lookups in a few seconds—GitHub, vendor API, redirect chain—then holds one long connection open.

A practical mitigation has two parts. First, ensure upstream DNS servers are reachable through the policy path you expect for general browsing, and avoid resolver chains that intermittently drop international queries. Second, consider targeted policies—commonly nameserver-policy in Mihomo-compatible cores—for suffixes you see repeatedly in MCP traffic. Always verify keys against the documentation bundled with your exact core build instead of copying aged forum snippets.

When DNS fixes clear most symptoms without changing proxy groups, you have strong evidence the bottleneck was resolution, not bandwidth. That distinction tells you whether to invest in resolver hygiene or in exit stability next.

8. System proxy versus TUN for Cursor helpers

System proxy is the lighter-touch option when the OS honors proxy settings and Electron-style helpers respect them for TLS-heavy control traffic. The familiar failure mode mirrors browsers: the primary document succeeds, yet secondary hosts bypass the proxy, leaving downloads or SSE feeds empty.

TUN mode pushes routing deeper so fewer executables can silently skirt Clash. If you already walked through our TUN mode guide, repeat the experiment while sorting connections for Cursor-related process names. TUN is not mandatory for everyone, but it is the right lever when evidence shows MCP helper traffic never appeared in the proxy log even though packets left the machine.

Regardless of mode, confirm the GUI is using the profile you edited. Editing one YAML while another snapshot remains selected manufactures phantom regressions that have nothing to do with Cursor MCP infrastructure.

9. Rule snippets: explicit coverage and clean ordering

The YAML fragments below illustrate steering traffic to a proxy group named PROXY. Rename that token to match your real policy label and insert these lines before broad provider rules that might prematurely return DIRECT for “domestic” CDNs that GitHub also uses.

# Example only — replace PROXY; verify suffixes against your Mihomo logs
rules:
  - DOMAIN-SUFFIX,github.com,PROXY
  - DOMAIN-SUFFIX,githubusercontent.com,PROXY
  - DOMAIN-SUFFIX,github.io,PROXY
  - DOMAIN,api.github.com,PROXY
  - DOMAIN-SUFFIX,your-mcp-vendor.example,PROXY

Prefer DOMAIN-SUFFIX when you can express intent precisely. Reserve DOMAIN-KEYWORD for noisy vendor patterns you cannot enumerate, because substring matches are powerful and easy to overfit. For vendor-specific SSE clusters, prefer the exact host you see in logs over wildcards that might swallow unrelated traffic.

If your subscription injects aggressive geo rules, duplicate critical GitHub lines in a user-controlled section that loads with correct precedence, or merge providers thoughtfully so your exceptions win. The same structural advice appears in our macOS Terminal proxy environment guide, which stresses that Git operations and HTTPS downloads share DNS expectations with developer tools.

10. SSE-specific pitfalls under mandatory proxy

SSE looks like trivial HTTP on paper, yet operations teams learn otherwise. Middle proxies may buffer server events until the buffer fills, defeating real-time semantics. Some corporate appliances strip chunked transfer encodings or impose short idle timers on long responses. When MCP worked from home but fails on office Wi-Fi with identical YAML, suspect path-dependent middleboxes before you blame the MCP author.

From a Clash perspective, the dominant issue is still policy coherence. If the initial POST succeeds through exit A while the long-lived stream accidentally migrates to exit B after an auto selector refresh, the session collapses even though each hop “looked healthy” in isolation. Pin vendor MCP destinations to stable providers, reduce hyperactive failover on those suffixes, and avoid stacking multiple VPN-class products that re-encapsulate the same flow.

For background on protocol behavior under loss, read Shadowsocks vs Trojan vs Hysteria2. The goal is to match transport characteristics to your packet-loss profile for long streams, not to crown a single global winner.

11. Verification commands that survive copy-paste culture

GUI logs win for breadth, yet terminal checks win for crisp reproducibility. When you suspect GitHub proxy issues, run a short curl probe through the same environment Cursor inherits. If you are on macOS or Linux and already export proxy variables for other dev tools, align with the patterns in our terminal guide; on Windows, verify whether PowerShell inherits system proxy or needs explicit variables.

# Example: replace with a small public object you are allowed to fetch
curl -I https://api.github.com/zen
curl -I https://raw.githubusercontent.com/octocat/Hello-World/master/README

Pair those probes with Mihomo rows captured at the same second. If curl shows a fast 200 while Cursor still spins, you have split-brain evidence: the IDE helper is not using the same proxy path as your shell. Fix visibility before you rewrite rules.

For TLS-only mysteries, openssl s_client -connect host:443 -servername host remains valuable when allowed by policy. It separates certificate path issues from HTTP-level quirks. Document the output hash or issuer line when opening vendor tickets so engineers can compare against expected pins.

12. GUI workflow: Mihomo logs as the source of truth

Desktop clients such as Clash Verge Rev expose live connections, DNS panes, and rule editors side by side. When Cursor MCP misbehaves, filter connections for github and your vendor substring, then read the chosen policy per row. If anything sensitive shows DIRECT while similar hosts use PROXY, fix precedence before swapping servers.

If the baseline install still feels unfamiliar, follow the Clash Verge Rev setup guide to confirm ports, subscriptions, and first launch before you chase MCP-specific ghosts.

13. How this differs from Marketplace-only routing

Our Cursor Marketplace split routing article focuses on extension delivery, editor shell CDNs, and inline model access patterns. Those issues still matter, yet remote MCP adds GitHub-shaped downloads and vendor-specific SSE long streams that rarely show up in Marketplace-only captures. Treat the two guides as complementary chapters in the same AI toolchain book rather than competing duplicates.

Enterprise readers should remember that split-horizon DNS can make international GitHub surfaces look broken even when Clash is perfect. If only MCP-facing domains fail while unrelated HTTPS succeeds, involve the network team with connection logs rather than assuming the proxy core is misconfigured.

14. Antivirus, TLS inspection, and dual VPN stacks

Third-party “optimizers,” HTTPS-filtering antivirus suites, and aggressive browser extensions sometimes reorder traffic in ways Clash cannot see. Disable them briefly during triage. Running two VPN-class products simultaneously invites routing loops that masquerade as application bugs.

If you also use WSL or containers alongside Cursor, remember those environments inherit none of your host YAML unless you explicitly bridge them—our WSL2 host-proxy guide covers the Linux side, which can confuse diagnostics when you test with curl from Ubuntu while MCP runs natively.

15. Open source and trust

If you want to inspect upstream source, review issues, or contribute patches, visit the community repositories linked from our docs. Keep that separate from day-to-day install paths: the primary way readers should fetch maintained desktop builds remains this site’s download flow, not a raw release asset buried in a thread.

16. Close with evidence, not superstition

Cursor MCP over HTTP and SSE fails loudly in production yet quietly in the UI. Treat every endless spinner as a prompt to open Mihomo, read policies row by row, and reconcile DNS with the hostnames Cursor actually contacted. Coherent Clash split routing across GitHub proxy classes, vendor control planes, and stable long-lived streams is the mechanical layer; disciplined exit choice is the polish once TCP and TLS agree.

Compared with toggling random VPNs, a maintained desktop client with Mihomo integration keeps diagnostics visible and reduces YAML foot-guns when vendors shift SSE edges overnight. → Download Clash for free and experience the difference