A working MCP server can still fail review because approval may cover more than its code: publisher eligibility, package contents, metadata, authentication, documentation, tool behavior, or a destination’s own policies. The rejection notice and the identity of the reviewer are essential to finding the actual cause; without them, a small code diff alone does not reveal what failed.
First identify who rejected the integration
“MCP integration” does not point to one universal approval process. A protocol client checking interoperability, the upstream MCP Registry, a client marketplace, a certification authority, and a private enterprise catalog may each evaluate different things. The MCP project says downstream marketplaces can apply their own criteria to Registry data, so being listed upstream does not guarantee acceptance or discoverability everywhere. See the MCP Registry announcement.
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| Review path | What may be evaluated | Useful evidence |
|---|---|---|
| Protocol client | Whether the server and client can communicate using compatible protocol behavior and versions. | Client/server versions, connection logs, and the exact failing interaction. |
| Upstream Registry | Registry submission requirements and submitted listing data. | Submission details and any validation result provided by the Registry. |
| Client marketplace | Registry information plus criteria chosen by that marketplace. | The marketplace’s rejection notice and listing requirements. |
| Certification authority | Eligibility, package, configuration, functionality, and other review requirements. Microsoft documents such a process for Copilot Studio. | Certification validation output, review notice, submitted package, and test setup. |
| Private or enterprise catalog | The organization’s own admission rules and security or operational requirements. | The administrator’s rejection details and applicable internal policy. |
These paths are not interchangeable: compatibility with an MCP client is not the same as approval for a particular distribution channel.
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Why a certification can fail when server code barely changes
Microsoft’s documented MCP server certification process illustrates how review can extend beyond implementation. Its requirements include a verified publisher, control of the endpoint, a complete OpenAPI definition, authentication settings, metadata, and intro.md documentation. Automated validation checks schema correctness, metadata completeness, packaging integrity, and baseline policy compliance. Microsoft then conducts a manual review of functionality, security, compliance, telemetry, and responsible-AI readiness; tools are tested using the credentials provided.
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That means a server can appear to work in one environment while its submission fails for a missing or incomplete artifact, an identity or endpoint issue, an authentication configuration problem, or a tool that does not behave as expected under the reviewer’s credentials. Microsoft’s process is one concrete example, not evidence that every marketplace or rejection uses the same checklist. See Microsoft’s MCP server certification requirements.
Match the rejection wording to the failure layer
Publisher or endpoint eligibility
If the notice mentions publisher verification, ownership, or endpoint control, inspect the submitting account and the relationship between that publisher and the endpoint. A code change will not resolve an eligibility or ownership issue.
Package, schema, metadata, or documentation
If validation identifies a schema error, incomplete metadata, packaging problem, or missing documentation, compare the rejected submission itself with the stated requirements. Confirm that the package and metadata are complete and consistent; changing server logic may be unnecessary.
Authentication or OAuth configuration
A successful local tool call does not prove that a review’s authorization flow is configured correctly. The MCP authorization security considerations require a server to validate tokens for its own audience and prohibit forwarding a client token to an upstream API. They also specify HTTPS endpoints, PKCE checks, and exact redirect-URI validation. Compare your authorization setup with the specification version implemented by both the server and the client, rather than assuming a generic OAuth configuration is sufficient. See the MCP authorization specification.
Tool behavior under review credentials
If the issue concerns functionality, reproduce the reviewer’s setup as closely as the notice allows. Check the submitted credentials, the specific tool call or sequence that failed, and the behavior returned to the client. A server that works with a developer’s own account may not work with the credentials supplied for testing.
Security, compliance, telemetry, or responsible-AI review
These concerns may involve how the integration handles data and operates, rather than whether the protocol connection succeeds. Ask for the specific finding and evidence; do not infer a code defect from a general review outcome.
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Check protocol versions before changing the implementation
Record the deployed server version, the client version, and the protocol version each supports. The MCP project’s July 28, 2026 release announcement describes breaking changes, including removal of the initialize handshake and session ID and the addition of required transport headers. A version mismatch can therefore affect behavior even if the server’s application logic has not changed.
Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteDo not adopt a newer protocol release automatically: first confirm which version the reviewing platform supports and which version the deployed client expects. The release announcement establishes that changes occurred; it does not establish that any particular rejection was caused by them.
Use the rejection notice to choose the smallest defensible fix
- Identify the reviewing destination. Determine whether the rejection came from a client, the upstream MCP Registry, a client marketplace, a certification program, or an enterprise administrator. Find that destination’s applicable requirements.
- Get the exact finding. Inspect the full rejection text and any validation report. If the notice is vague, request the failed check, affected artifact or tool, and reproduction details.
- Gather the submitted evidence. Keep the exact manifest or package, metadata, documentation, endpoint and authentication configuration, test credentials where appropriate, and deployed protocol versions used for review.
- Classify the failure. Decide whether the evidence points to publisher eligibility, package or schema, authentication, version compatibility, tool behavior, or a manual security or policy review.
- Change only the implicated layer, then validate again. A package correction, OAuth adjustment, publisher-account fix, listing update, or server implementation change may each be appropriate in a different case. Confirm the stated failure is resolved before resubmitting.
Without the rejection notice and the reviewing platform, it is not possible to identify this integration’s root cause or promise that a particular minimal fix will work. The useful distinction is whether the failed check concerns the server itself or something surrounding its submission and approval.
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