Streamable HTTP MCP client fails to parse valid SSE initialize response
Open 💬 1 comment Opened Jun 8, 2026 by fcrhu
What version of Codex CLI is running?
codex-cli 0.137.0
What subscription do you have?
ChatGPT Pro
Which model were you using?
gpt-5.5
What platform is your computer?
Microsoft Windows NT 10.0.26200.0 x64
What terminal emulator and version are you using (if applicable)?
Codex app integrated terminal / Windows PowerShell 5.1.26100.8457
Codex doctor report
{
"schemaVersion": 1,
"generatedAt": "1780916587s since unix epoch",
"overallStatus": "ok",
"codexVersion": "0.137.0",
"checks": {
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"category": "app-server",
"status": "ok",
"summary": "background server is not running",
"details": {
"control socket": "C:\\Users\\<user>\\.codex\\app-server-control\\app-server-control.sock",
"daemon state dir": "C:\\Users\\<user>\\.codex\\app-server-daemon",
"mode": "ephemeral",
"pid file": "C:\\Users\\<user>\\.codex\\app-server-daemon\\app-server.pid (missing)",
"settings": "C:\\Users\\<user>\\.codex\\app-server-daemon\\settings.json (missing)",
"status": "not running",
"update-loop pid file": "C:\\Users\\<user>\\.codex\\app-server-daemon\\app-server-updater.pid (missing)"
},
"remediation": null,
"durationMs": 0
},
"auth.credentials": {
"id": "auth.credentials",
"category": "auth",
"status": "ok",
"summary": "auth is configured",
"details": {
"auth file": "C:\\Users\\<user>\\.codex\\auth.json",
"auth storage mode": "File",
"stored API key": "false",
"stored ChatGPT tokens": "true",
"stored agent identity": "false",
"stored auth mode": "chatgpt"
},
"remediation": null,
"durationMs": 0
},
"config.load": {
"id": "config.load",
"category": "config",
"status": "ok",
"summary": "config loaded",
"details": {
"CODEX_HOME": "C:\\Users\\<user>\\.codex",
"config.toml": "C:\\Users\\<user>\\.codex\\config.toml",
"config.toml parse": "ok",
"cwd": "c:\\deploy",
"enabled feature flags": "shell_tool, shell_snapshot, terminal_resize_reflow, sqlite, hooks, enable_request_compression, multi_agent, apps, tool_suggest, plugins, in_app_browser, browser_use, browser_use_external, computer_use, plugin_sharing, image_generation, skill_mcp_dependency_install, steer, guardian_approval, goals, collaboration_modes, tool_call_mcp_elicitation, personality, fast_mode, tui_app_server, workspace_dependencies",
"feature flag overrides": "none",
"feature flags enabled": "26",
"log dir": "C:\\Users\\<user>\\.codex\\log",
"mcp servers": "2",
"model": "gpt-5.5",
"model provider": "openai",
"sqlite home": "C:\\Users\\<user>\\.codex"
},
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},
"git.environment": {
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"details": {
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"git build options": "git version 2.54.0.windows.1; cpu: x86_64; built from commit: 2b8a3ab140826ac423c2845ef81d4c6ac4f7bf3c; sizeof-long: 4; sizeof-size_t: 8; shell-path: D:/git-sdk-64-build-installers/usr/bin/sh; rust: disabled; feature: fsmonitor--daemon; gettext: enabled; libcurl: 8.19.0; OpenSSL: OpenSSL 3.5.6 7 Apr 2026; zlib: 1.3.2; SHA-1: SHA1_DC; SHA-256: SHA256_BLK; default-ref-format: files; default-hash: sha1",
"git exec path": "C:/Program Files/Git/mingw64/libexec/git-core",
"git version": "git version 2.54.0.windows.1",
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"installation": {
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"status": "ok",
"summary": "installation looks consistent",
"details": {
"PATH codex #1": "C:\\Users\\<user>\\AppData\\Roaming\\npm\\codex",
"PATH codex #2": "C:\\Users\\<user>\\AppData\\Roaming\\npm\\codex.cmd",
"PATH codex entries": "2",
"current executable": "C:\\Users\\<user>\\AppData\\Roaming\\npm\\node_modules\\@openai\\codex\\node_modules\\@openai\\codex-win32-x64\\vendor\\x86_64-pc-windows-msvc\\bin\\codex.exe",
"install context": "npm (package C:\\Users\\<user>\\AppData\\Roaming\\npm\\node_modules\\@openai\\codex\\node_modules\\@openai\\codex-win32-x64\\vendor\\x86_64-pc-windows-msvc, bin C:\\Users\\<user>\\AppData\\Roaming\\npm\\node_modules\\@openai\\codex\\node_modules\\@openai\\codex-win32-x64\\vendor\\x86_64-pc-windows-msvc\\bin, resources C:\\Users\\<user>\\AppData\\Roaming\\npm\\node_modules\\@openai\\codex\\node_modules\\@openai\\codex-win32-x64\\vendor\\x86_64-pc-windows-msvc\\codex-resources, path C:\\Users\\<user>\\AppData\\Roaming\\npm\\node_modules\\@openai\\codex\\node_modules\\@openai\\codex-win32-x64\\vendor\\x86_64-pc-windows-msvc\\codex-path)",
"managed by bun": "false",
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},
"remediation": null,
"durationMs": 227
},
"mcp.config": {
"id": "mcp.config",
"category": "mcp",
"status": "ok",
"summary": "MCP configuration is locally consistent",
"details": {
"configured servers": "2",
"disabled servers": "0",
"stdio servers": "1",
"streamable_http servers": "1"
},
"remediation": null,
"durationMs": 138
},
"network.env": {
"id": "network.env",
"category": "network",
"status": "ok",
"summary": "network-related environment looks readable",
"details": {
"proxy env vars": "none"
},
"remediation": null,
"durationMs": 0
},
"network.provider_reachability": {
"id": "network.provider_reachability",
"category": "reachability",
"status": "ok",
"summary": "active provider endpoints are reachable over HTTP",
"details": {
"ChatGPT base URL": "https://chatgpt.com/backend-api/ reachable (HTTP 403)",
"reachability mode": "ChatGPT auth"
},
"remediation": null,
"durationMs": 81
},
"network.websocket_reachability": {
"id": "network.websocket_reachability",
"category": "websocket",
"status": "ok",
"summary": "Responses WebSocket handshake succeeded",
"details": {
"DNS": "2 IPv4, 0 IPv6, first IPv4",
"auth mode": "chatgpt",
"connect timeout": "15000 ms",
"endpoint": "wss://chatgpt.com/backend-api/<redacted>",
"handshake result": "HTTP 101 Switching Protocols",
"model provider": "openai",
"models etag present": "true",
"provider name": "OpenAI",
"proxy env vars": "none",
"reasoning header": "false",
"server model present": "false",
"supports websockets": "true",
"wire API": "responses"
},
"remediation": null,
"durationMs": 902
},
"runtime.provenance": {
"id": "runtime.provenance",
"category": "runtime",
"status": "ok",
"summary": "running npm on windows-x86_64",
"details": {
"commit": "unknown",
"current executable": "C:\\Users\\<user>\\AppData\\Roaming\\npm\\node_modules\\@openai\\codex\\node_modules\\@openai\\codex-win32-x64\\vendor\\x86_64-pc-windows-msvc\\bin\\codex.exe",
"install method": "npm (package C:\\Users\\<user>\\AppData\\Roaming\\npm\\node_modules\\@openai\\codex\\node_modules\\@openai\\codex-win32-x64\\vendor\\x86_64-pc-windows-msvc, bin C:\\Users\\<user>\\AppData\\Roaming\\npm\\node_modules\\@openai\\codex\\node_modules\\@openai\\codex-win32-x64\\vendor\\x86_64-pc-windows-msvc\\bin, resources C:\\Users\\<user>\\AppData\\Roaming\\npm\\node_modules\\@openai\\codex\\node_modules\\@openai\\codex-win32-x64\\vendor\\x86_64-pc-windows-msvc\\codex-resources, path C:\\Users\\<user>\\AppData\\Roaming\\npm\\node_modules\\@openai\\codex\\node_modules\\@openai\\codex-win32-x64\\vendor\\x86_64-pc-windows-msvc\\codex-path)",
"platform": "windows-x86_64",
"version": "0.137.0"
},
"remediation": null,
"durationMs": 0
},
"runtime.search": {
"id": "runtime.search",
"category": "search",
"status": "ok",
"summary": "search is OK (bundled)",
"details": {
"search command": "C:\\Users\\<user>\\AppData\\Roaming\\npm\\node_modules\\@openai\\codex\\node_modules\\@openai\\codex-win32-x64\\vendor\\x86_64-pc-windows-msvc\\codex-path\\rg.exe",
"search command readiness": "file exists",
"search provider": "bundled"
},
"remediation": null,
"durationMs": 0
},
"sandbox.helpers": {
"id": "sandbox.helpers",
"category": "sandbox",
"status": "ok",
"summary": "sandbox configuration is readable",
"details": {
"approval policy": "OnRequest",
"codex-linux-sandbox helper": "none",
"execve wrapper helper": "none",
"filesystem sandbox": "restricted",
"network sandbox": "restricted"
},
"remediation": null,
"durationMs": 0
},
"state.paths": {
"id": "state.paths",
"category": "state",
"status": "ok",
"summary": "state paths and databases are inspectable",
"details": {
"CODEX_HOME": "C:\\Users\\<user>\\.codex (dir)",
"active rollout files": "84 files, 59208961 total bytes, 704868 average bytes",
"archived rollout files": "0 files, 0 total bytes, 0 average bytes",
"goals DB": "C:\\Users\\<user>\\.codex\\goals_1.sqlite (file)",
"goals DB integrity": "ok",
"log DB": "C:\\Users\\<user>\\.codex\\logs_2.sqlite (file)",
"log DB integrity": "ok",
"log dir": "C:\\Users\\<user>\\.codex\\log (missing)",
"memories DB": "C:\\Users\\<user>\\.codex\\memories_1.sqlite (file)",
"memories DB integrity": "ok",
"sqlite home": "C:\\Users\\<user>\\.codex (dir)",
"state DB": "C:\\Users\\<user>\\.codex\\state_5.sqlite (file)",
"state DB integrity": "ok"
},
"remediation": null,
"durationMs": 451
},
"state.rollout_db_parity": {
"id": "state.rollout_db_parity",
"category": "threads",
"status": "ok",
"summary": "rollout files and state DB thread inventory agree",
"details": {
"default model provider": "openai",
"rollout DB active files": "84",
"rollout DB active rows": "84",
"rollout DB archive mismatches": "0",
"rollout DB archived files": "0",
"rollout DB archived rows": "0",
"rollout DB duplicate DB paths": "0",
"rollout DB duplicate rollout thread ids": "0",
"rollout DB malformed file names": "0",
"rollout DB missing active rows": "0",
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"rollout DB model providers": "openai=84",
"rollout DB rows": "84",
"rollout DB scan cap reached": "false",
"rollout DB scan errors": "0",
"rollout DB sources": "vscode=54, subagent:other=30",
"rollout DB stale rows": "0"
},
"remediation": null,
"durationMs": 410
},
"system.environment": {
"id": "system.environment",
"category": "system",
"status": "ok",
"summary": "OS language en-US",
"details": {
"os": "Windows 10.0.26200 (Windows 11 Professional) [64-bit]",
"os language": "en-US",
"os type": "Windows",
"os version": "10.0.26200"
},
"remediation": null,
"durationMs": 0
},
"terminal.env": {
"id": "terminal.env",
"category": "terminal",
"status": "ok",
"summary": "terminal metadata was detected",
"details": {
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"console input code page": "850",
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"terminal.title": {
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"durationMs": 0
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"updates.status": {
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"status": "ok",
"summary": "update configuration is locally consistent",
"details": {
"check for update on startup": "true",
"latest version": "0.137.0",
"latest version status": "current version is not older",
"npm update target": "C:\\Users\\<user>\\AppData\\Roaming\\npm\\node_modules\\@openai\\codex",
"update action": "npm install -g @openai/codex",
"version cache": [
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"missing"
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"remediation": null,
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}
}
}What issue are you seeing?
Codex fails to initialize the Atlassian remote MCP server even though OAuth succeeds and the server returns a valid MCP initialize response over text/event-stream.
MCP server:
- Name:
atlassian - URL:
https://mcp.atlassian.com/v1/mcp/authv2 - Transport:
streamable_http - Auth: OAuth
The visible error is:
MCP startup failed: handshaking with MCP server failed:
Send message error Transport [...] error:
Deserialize error: data did not match any variant of untagged enum JsonRpcMessage,
when send initialize request
What steps can reproduce the bug?
- Use Codex CLI
0.137.0on Windows.
- Configure the Atlassian MCP server:
``toml``
[mcp_servers.atlassian]
url = "https://mcp.atlassian.com/v1/mcp/authv2"
- Authenticate the MCP server:
``powershell``
codex mcp login atlassian
- Confirm that the server is enabled:
``powershell``
codex mcp list
The output shows:
``text``
atlassian https://mcp.atlassian.com/v1/mcp/authv2 enabled OAuth
- Start Codex with this MCP server enabled, or try to use the Atlassian MCP server from an existing Codex session.
- Observe that Codex fails during MCP initialization with:
``text``
Deserialize error: data did not match any variant of untagged enum JsonRpcMessage,
when send initialize request
- As a control check, manually replay the MCP
initializerequest against the same endpoint and OAuth credential. The server returnsHTTP 200 OKwithContent-Type: text/event-stream, and the SSEdata:payload contains a valid JSON-RPC initialize response.
What is the expected behavior?
Codex should successfully initialize the Atlassian Streamable HTTP MCP server and expose its tools.
When the MCP server responds to the initialize request with Content-Type: text/event-stream, Codex should parse the SSE event stream, extract the JSON-RPC message from the data: line, and deserialize that JSON-RPC payload.
In this case, the server returns a valid JSON-RPC initialize response inside the SSE data: payload, so initialization should complete and tools such as createJiraIssue should become available.
Additional information
A manual HTTP replay of the MCP initialize request using the same OAuth credential succeeds.
The Atlassian MCP server responds with:
HTTP 200 OK
Content-Type: text/event-stream
Mcp-Session-Id: <present>The response body is an SSE message:
event: message
data: {"result":{"protocolVersion":"2025-06-18","capabilities":{"logging":{},"tools":{"listChanged":true},"resources":{}},"serverInfo":{"name":"atlassian-mcp-server","version":"1.0.0"}},"jsonrpc":"2.0","id":1}If I extract the JSON from the SSE data: line, it parses as a valid JSON-RPC response:
{
"StatusCode": 200,
"ContentType": "text/event-stream",
"HasSessionId": true,
"LooksLikeSse": true,
"ExtractedJsonRpc": "2.0",
"ExtractedId": 1,
"ServerName": "atlassian-mcp-server",
"ProtocolVersion": "2025-06-18"
}Suspected cause: the Codex Streamable HTTP MCP client appears to deserialize the full SSE envelope as JsonRpcMessage instead of first parsing the SSE event and then deserializing the JSON payload from the data: line.
This looks related to #13920, #20982, and #21903, but the failure point is different: in this case Codex fails while parsing the valid text/event-stream response to the initial initialize request.
No OAuth tokens, cookies, or credential files are included here.
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