Cannot connect to remote MCP server - "Couldn't reach the MCP server"

[sakura20260508]

Problem

When clicking the "Connect" button after adding the freee MCP connector in Claude.ai, the following error appears:

"Couldn't reach the MCP server. You can check the server URL and verify the server is running."

Environment

• MCP Server URL: https://mcp.freee.co.jp/mcp
• Client: Claude.ai (browser)

Steps to reproduce

1. Add custom connector in Claude.ai with URL: https://mcp.freee.co.jp/mcp
2. Click "Connect" button
3. Error appears immediately

Error reference numbers

• ofid_bcb98ddc0eede490
• ofid_701e90d4f72b2771

[JeongJaeSoon]

Hi @sakura20260508 — thanks for the detailed report. We've identified the root cause, deployed an immediate fix to production, and verified that new connections succeed.

What to do right now

If you're still seeing "Couldn't reach the MCP server," please:

1. Open Claude.ai → Settings → Connectors.
2. Remove the existing freee MCP connector entry.
3. Re-add it with the same URL: https://mcp.freee.co.jp/mcp.
4. Click Connect again.

We've confirmed on our side that this flow now completes successfully. The remove-then-re-add step is needed because Claude.ai caches the previous failed registration on the client side; deleting the connector forces a fresh DCR (/register) call against the server, which now goes through.

Root cause

In v0.25.5 (PR #426) we enabled an IP-based rate limiter by default. The /register endpoint, which Claude.ai hits during the OAuth Dynamic Client Registration step of "Connect," carried a strict per-IP limit.

Claude.ai's traffic appears to originate from a limited set of shared client-side egress IPs (typical for vendor-hosted MCP clients), so that budget was exhausted across the global user base almost immediately. Subsequent registrations received HTTP 429, which Claude.ai surfaces as "Couldn't reach the MCP server."

Immediate fix (already deployed)

We've adjusted the production rate-limiting configuration on mcp.freee.co.jp so that legitimate Claude.ai traffic is no longer rejected. Edge-layer protections remain in place. We've verified end-to-end that fresh Connect flows from Claude.ai now complete successfully.

Longer-term fix

The IP-based key is fundamentally incompatible with vendor-aggregated traffic on pre-auth endpoints. We're planning a follow-up that redesigns the keying so vendor-aggregated /register traffic doesn't share a single counter with abusive traffic, and shifts post-authentication limits to per-client / per-token keys. We'll open a separate issue tracking that work and cross-link it here.

If it still doesn't work

If the steps above don't resolve it for you, please reply with details of the failing attempt (timestamp in UTC and the browser / client you're using) and we'll investigate.

Apologies for the disruption, and thanks again for the report.

[sakura20260508]

Dear @JeongJaeSoon —Thank you so much for the quick fix! I followed your steps (remove → re-add → connect) and it worked perfectly. I can now use freee MCP with Claude. Really appreciate your detailed explanation of the root cause as well!

[JeongJaeSoon]

@him0

まだ根本対策ができておらず、Issue としては Open しておきたいです。来週中に修正PRを作成し、Rate Limitを再度有効化する予定です