MCP servers that share state across IDEs: one mechanism, six ways it quietly stops
Does the memory follow you when you switch editors? Write something in Cursor, open Claude Code an hour later, and for most persistent memory MCP servers the honest answer is: it depends on one setup step you probably did not know mattered. This article checks six vendors, including our own, Mnemoverse, not for whether they claim cross-IDE sharing, but for the specific, silent way each one can stop sharing while every connected client still says connected.
TL;DR
- The mechanism is identical everywhere. One account, several client apps, one backend. No vendor checked here, ours included, does anything more sophisticated than that.
- The failure mode is what differs. A key from the wrong account or a domain filter on Mnemoverse; mismatched IDs across Mem0 integrations; Cognee left in Standalone Mode instead of API Mode; inconsistent container tags on Supermemory; an undocumented scenario for Graphiti; no claim at all from Letta.
- The connected indicator never catches any of these. Every failure below happens with every client reporting a healthy connection, which is why the check at the end is a data check, not a status check.
- Disclosure: Mnemoverse is one of the six vendors compared, built by this site's publisher. Every fact here, ours included, comes from a page the vendor published, fetched the week this article was checked.
The mechanism is the same everywhere
Strip the marketing off any of these products and cross-IDE sharing reduces to one sentence: one account, several client applications, all pointed at the same backend. That is all of it. The interesting question was never how the syncing works, because the answer is always the same. The interesting question is which setup step, if skipped or done inconsistently, leaves two clients that both show connected without sharing anything, and how you would ever notice.
Mnemoverse: sharing is the default, and the two ways to defeat it
Mnemoverse removes the setup step most vendors leave in. One API key, and every connected client already shares, by default rather than as a mode to discover: "If you already have a key from Claude Code or ChatGPT, use the same one. That's the point: same key, same memory, every tool" (editors guide). The VS Code path can also connect without a key, over a remote URL with OAuth sign-in ("This is verified working on VS Code Desktop", VS Code guide), and it lands in the same account system as every key-based client.
Two ways to defeat this, named directly because they are ours.
The key is the account. A key created in a different console account connects perfectly and returns that account's store, typically empty, and none of your shared rooms, with no error anywhere: the client says connected, the memory is simply someone else's. The same holds for the keyless path, which signs into whatever account the browser holds. Cross-tool sharing is a property of the account, so the check is not whether each client is connected but whether each is connected as the same account. This is the failure mode we found on our own setup while checking this article, and the Claude Code guide's troubleshooting section now names it.
Domains are a filter you can turn into a silo. Reads default to your own domains, unfiltered. If a team adopts the convention of writing with a separate domain per tool and later filters reads by that same domain, it has built its own partition. Not a product limitation, something a user can do to themselves, and the fix is to stop filtering.
Cognee: two modes, one word apart
Cognee names its own trap more precisely than any vendor here, and it is easy to conflate with a second list on the same page. Its MCP server has two Architecture Modes that determine sharing, not to be confused with the three Setup Options the same page lists for how you get it running: Docker Quickstart, API Mode (Shared), Local Setup.
The two architecture modes, verbatim from docs.cognee.ai/cognee-mcp/mcp-overview: "Standalone Mode: The MCP server manages its own database and processing. Each MCP instance maintains separate data." And: "API Mode: The MCP server connects to a centralized Cognee backend via API. Multiple MCP instances can share the same knowledge graph."
This is a documented, deliberate design, personal development kept separate from team sharing, not a defect. But the page names no default mode, so someone installing per client, expecting the cross-tool memory the category's marketing promises, can land in Standalone Mode's isolated graphs and has to know the two-mode distinction exists before going to look for it.
Mem0: scoped by you, not by them
Mem0 documents cross-tool sharing explicitly: a hosted MCP endpoint, several clients on one URL. The silent failure mode is equally explicit, in the vendor's own words, once more than one participant writes into the same memory: "You control which speaker a memory belongs to by scoping each add() call with user_id, agent_id, and run_id; Mem0 does not infer that scope automatically from the conversation" (group chat docs). If two integrations pass different values for what should be the same person, they get two memory pools that never merge, silently, with no error.
Supermemory: the same key is not enough, the tag has to match too
Supermemory makes the loudest, most repeated version of the claim: "Record something in Claude, recall it in Cursor. Your context follows you across every tool, no sync, no export, no copy-paste" (supermemory.ai/mcp). The mechanism is real and has two parts: the same API key across clients, and a consistent container tag, the scope every memory is written under and read from. The vendor's own docs call the tag "an authorization boundary, not just an organizational one" and state that a memory under one tag lives "completely separate" from memories under another unless you explicitly query across both (container tags). The failure mode lives in that second part. Two clients on the same key but different container tags are two isolated memories that both say connected, the same shape as Mem0's mismatched identifiers, one level up. The pricing page, checked live, lists the plugins and the MCP server under the free plan, so plan access is not the gate here; the tag is.
Letta and Graphiti: two honest gaps
Letta's own documentation makes no first-party claim about third-party tool interop at all, in either direction. If the question is whether memory follows you from Cursor to Claude Code, Letta's docs simply never say.
Graphiti, the open-source half of Zep, has its own MCP server, and pointing two clients at the same running instance is architecturally plausible: nothing in the design forbids it. But no page states multi-client sharing as a tested scenario, and this article treats that as an open gap, not an inferred yes.
Zep's hosted product, by contrast, is the cleanest single-mode claim of the six vendors: cross-client sharing, stated directly, no caveat found (the vendor facts behind that reading are in the companion comparison).
The table
Six vendors, seven rows: Zep's hosted product and its open-source half behave differently enough to be read separately.
| claims cross-IDE sharing | the concrete way it can silently not happen | |
|---|---|---|
| Mnemoverse | yes, default behavior | a key issued to a different account (connected, empty, no error); or a per-tool domain filter the user adds themselves |
| Mem0 | yes, hosted MCP | user_id, agent_id, run_id scoped inconsistently across integrations |
| Cognee | yes, mode-dependent | Standalone Mode left in place per client instead of API Mode |
| Supermemory | yes, explicit and repeated | container tags inconsistent across clients on the same key |
| Zep (hosted) | yes, explicit | none found; the clearest single-mode claim here |
| Graphiti (self-hosted) | plausible, not documented as tested | no stated failure mode because no stated success mode either |
| Letta | no claim either way | third-party tool interop is simply undocumented |
Check your own setup
Same account, same key, across every client, checked with data rather than with a green checkmark: write a marker from one tool and read it back from the other. For Mnemoverse: confirm every client is on the same account, then confirm no per-tool domain filter unless you added one deliberately. For Mem0: matching identifiers across every integration. For Cognee: API Mode, not Standalone, the moment more than one client needs the same graph. For Supermemory: the same container tag on every client, not only the same key.
Related
- Best Persistent Memory APIs Compared — the same six vendors on price, licence and self-hosting
- Claude Code guide — troubleshooting for the failure this article opens with
- Editors: one key, every tool — the setup this article assumes
Cross-client claims reused from this site's comparison of six persistent memory APIs, fetched 2026-09-01. This article's own new depth, the failure modes, Cognee's two-mode split, Mem0's manual scoping, Supermemory's tag scope and our own account-identity case, re-verified live 2026-09-03 with full browser headers. Two corrections against the working draft: Cognee's isolated mode is "Standalone Mode", not "Local Setup", and an earlier claim that Supermemory's pricing page contradicts its MCP page on free-tier plugins did not survive a live read, both pages list the plugins under the free plan. Mnemoverse's own facts fetched the same day from its editors guide and VS Code guide. No performance or benchmark number appears in this article, for any system, pending a completed clean benchmark run of our own.