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A rejected MCP integration may need little or no server-code change because approval can depend on the submission package, publisher identity, OAuth configuration, and the destination’s own review rules. But without the rejection notice and the name of the reviewer, there is no sound way to identify the cause in this case. Start by finding out who rejected it and which part of the submission they assessed.
First identify what “rejected” means
MCP compatibility and approval to appear in a particular directory or product are different things. A server can speak the protocol and still fail a marketplace’s listing requirements, a certification review, or an organization’s private approval process.
The MCP project describes an upstream Registry that provides data to downstream client marketplaces; those marketplaces may apply their own criteria. Microsoft’s certification process is a separate example, not a universal MCP approval standard. Identify the reviewer and submission track before changing code or applying another platform’s checklist.
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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minute| Review pathway | What may be assessed | Useful evidence to request or inspect |
|---|---|---|
| Protocol client | Whether the deployed client and server interoperate using supported protocol and transport behavior. | Client and server versions, connection logs, and the exact error. |
| Upstream Registry | Registry-specific submission requirements. | Registry validation output and the submitted entry. |
| Client marketplace | Its own listing or discovery criteria, which can go beyond upstream Registry data. | Marketplace rejection notice and listing requirements. |
| Certification authority | Potentially publisher eligibility, package, authentication, functionality, security, and policy requirements. | Validation report, review notice, submitted package, and test configuration. |
| Private or enterprise catalog | The organization’s own technical, security, and administrative requirements. | Administrator’s rejection reason and the relevant internal criteria. |
The MCP Registry project explains the distinction between registry data and downstream marketplace decisions in its Registry announcement.
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Why a small code diff can still leave a failed submission
Microsoft’s documented certification process illustrates how review can involve much more than the server implementation. It requires publisher verification and endpoint ownership, and calls for a submission package containing a complete OpenAPI definition, authentication settings, metadata, and intro.md documentation. Automated validation covers schema correctness, metadata completeness, packaging integrity, and baseline policy compliance. After that, Microsoft manually reviews functionality, security, compliance, telemetry, and responsible-AI readiness, testing tools with the credentials provided.
Those are Microsoft-specific certification details, not requirements to assume for every MCP destination. They show why an integration can fail approval while its code changes remain small: the problem could be in publisher identity, package contents, configuration, or review evidence rather than in tool logic. See Microsoft’s MCP server certification documentation for the requirements of that process.
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Check OAuth and authorization separately
A server that appears to connect successfully can still have an authorization problem. The MCP authorization security considerations specify that servers validate tokens for their own audience and do not pass a client token through to an upstream API. They also address HTTPS endpoints, PKCE checks, and exact redirect URI validation.
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Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →- Confirm the resource or audience in the access token is the MCP server that receives it, and that the server validates it before tool execution.
- Check that the server does not forward the client’s token as a credential to another API.
- Verify HTTPS use and the PKCE and redirect-URI settings required by the authorization flow.
- Compare the actual client and server configuration with the version of the authorization specification they implement; do not assume every platform uses the same setup.
Use the relevant version of the MCP authorization security considerations when diagnosing this layer.
Verify the protocol version before changing behavior
Protocol compatibility is another distinct failure layer. The MCP project’s release-candidate announcement dated July 28, 2026, documents breaking changes that include removing the initialize handshake and session ID and adding required transport headers. A change in one version is not automatically a requirement for every client or submission track: check the versions actually deployed and the version the reviewer supports before adapting the server.
The July 28, 2026 MCP release-candidate announcement describes those changes. Treat it as version-specific information, not a blanket instruction to upgrade.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Turn the rejection notice into a targeted fix
- Identify the reviewer and track. Determine whether the rejection came from a protocol client, the MCP Registry, a client marketplace, a certification authority, or an enterprise administrator.
- Get the exact failure evidence. Save the rejection wording, validator output, and any reported test failure. Ask which requirement failed if the notice is vague.
- Match the failure to its layer. Publisher or endpoint complaints point to identity and ownership; schema, package, or metadata errors point to submission artifacts; auth errors point to OAuth configuration; tool failures point to behavior under the submitted test credentials; policy findings point to the relevant security, compliance, telemetry, or responsible-AI review.
- Compare the submitted state with the tested state. Check the exact package or manifest, endpoint and auth settings, provided test credentials, and client/server protocol versions. A local fix is not enough if the resubmitted package or configuration is unchanged.
- Change only the implicated layer, then validate it. A server implementation fix, OAuth adjustment, package correction, publisher-account change, and marketplace listing update are different remedies. Use the reviewer’s evidence to choose among them rather than making unrelated code changes.
What can—and cannot—be concluded from the small diff
Little server-code change is consistent with a rejection caused by packaging, metadata, authentication configuration, publisher checks, or destination-specific review. It does not prove that any one of those caused this rejection. The platform, submission track, deployment details, and rejection message are needed to name a root cause or prescribe a minimal fix.
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