modelcontextprotocol/java-sdk

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The official Java SDK for Model Context Protocol servers and clients. Maintained in collaboration with Spring AI

Stars: 3.7k
Forks: 1.1k
Open beginner issues: 0
Indexed issues: 113
Avg merge: 1d 15h
Merged PRs (30d): 9

Dominant language: Java
License: MIT
Last GitHub push: Sep 18, 2026
Latest indexed: Sep 20, 2026
Contributing guide: Contributing guide
Code of conduct: Code of conduct
Beginner labels: good first issue help wanted

Beginner friendly Everything

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113 issues indexed so far

SSE client silently truncates a data: line at U+2028/U+2029/U+0085, then fails with "Error parsing JSON-RPC message" Open

area/transport bug P2

Difficulty 2/5 1-3 hours Newbie friendliness 88/100

modelcontextprotocol/java-sdk#1136 · Opened Sep 18, 2026
McpClientSession/McpServerSession: pending response entries leak when a request times out or is cancelled Open

area/client area/server area/transport bug P2

Difficulty 3/5 1-2 days Newbie friendliness 35/100

modelcontextprotocol/java-sdk#1133 · 1 comment · Opened Sep 13, 2026
Client request handlers that complete empty send no JSON-RPC response Open

area/client bug P2

Difficulty 2/5 1-3 hours Newbie friendliness 84/100

modelcontextprotocol/java-sdk#1124 · 1 comment · Opened Sep 3, 2026
ServerCapabilities.logging is added unconditionally, overriding the caller's explicit capabilities Open

bug P2 ready for work

Difficulty 2/5 1-3 hours Newbie friendliness 68/100

modelcontextprotocol/java-sdk#1086 · 1 comment · Opened Aug 11, 2026
listTools() and the other no-arg list*() methods follow the cursor chain without any bound Open

bug P3

Difficulty 4/5 3-5 days Newbie friendliness 38/100

modelcontextprotocol/java-sdk#1084 · 1 comment · Opened Aug 10, 2026
McpServerSession never sends a response when a request handler's Mono completes empty — violates JSON-RPC 2.0's one-response-per-request contract Open

bug P2 ready for work

Difficulty 4/5 3-5 days Newbie friendliness 68/100

modelcontextprotocol/java-sdk#1081 · 2 comments · Opened Aug 8, 2026
Add `transportContextProvider` to `McpClient.AsyncSpec` Open

area/client area/transport waiting for user

modelcontextprotocol/java-sdk#1075 · 3 comments · 1 assignee · Opened Aug 1, 2026
Request customizers can't tell which connection a request belongs to Open

area/client area/transport P3 waiting for user

modelcontextprotocol/java-sdk#1074 · 3 comments · 1 assignee · Opened Aug 1, 2026
Allow composing request customizers on the HTTP client transport builders Open

area/client area/transport P2

modelcontextprotocol/java-sdk#1073 · 2 comments · 1 reaction · 1 assignee · Opened Aug 1, 2026
Disable standalone GET SSE Stream option for Streamable HTTP client transport Open

enhancement P3

Difficulty 3/5 1-2 days Newbie friendliness 72/100

modelcontextprotocol/java-sdk#1068 · Opened Jul 21, 2026
Reject listRoots if not supported by client, without sending any request Open

enhancement good first issue P3

Difficulty 2/5 1-3 hours Newbie friendliness 82/100

modelcontextprotocol/java-sdk#1067 · Opened Jul 19, 2026
Migrate null annotations to jspecify Open

enhancement P2 ready for work

Difficulty 3/5 1-2 days Newbie friendliness 68/100

modelcontextprotocol/java-sdk#1066 · 1 comment · Opened Jul 18, 2026
Un-deprecate/add no-arg builders Open

enhancement needs confirmation P3

Difficulty 5/5 Over a week Newbie friendliness 42/100

modelcontextprotocol/java-sdk#1065 · Opened Jul 18, 2026
Expose API to inspect and remove inactive server sessions Open

area/server enhancement needs confirmation P2

Difficulty 5/5 Over a week Newbie friendliness 35/100

modelcontextprotocol/java-sdk#1063 · 2 comments · 1 reaction · Opened Jul 17, 2026
Stateful streamable server calls listRoots() unconditionally on roots/list_changed, blocking a servlet thread until requestTimeout when no roots consumer is registered Open

bug P2 ready for work

Difficulty 3/5 1-2 days Newbie friendliness 78/100

modelcontextprotocol/java-sdk#1061 · 2 comments · 1 reaction · Opened Jul 16, 2026
SSE client rejects valid `retry:` field and ignores reconnection timing (Streamable HTTP) Open

area/client area/transport P2 waiting for user

Difficulty 4/5 3-5 days Newbie friendliness 45/100

modelcontextprotocol/java-sdk#1047 · 2 comments · Opened Jun 30, 2026
Streamable HTTP client: slow reception of large SSE tool responses (fromLineSubscriber line-assembly bottleneck) Open

area/client area/transport enhancement P2

modelcontextprotocol/java-sdk#1042 · 3 comments · 1 assignee · Opened Jun 28, 2026
SEP-2663: Tasks Extension Open

enhancement extensions P2

Difficulty 5/5 Over a week Newbie friendliness 35/100

modelcontextprotocol/java-sdk#1013 · 2 comments · Opened Jun 6, 2026
SEP-2577: Deprecate Roots, Sampling, and Logging Open

area/client area/server enhancement P1 ready for work

Difficulty 4/5 3-5 days Newbie friendliness 35/100

modelcontextprotocol/java-sdk#1012 · Opened Jun 6, 2026
SEP-2575: Make MCP Stateless Open

area/transport enhancement P1

Difficulty 5/5 Over a week Newbie friendliness 25/100

modelcontextprotocol/java-sdk#1011 · 10 comments · 8 reactions · Opened Jun 6, 2026
SEP-2567: Sessionless MCP via Explicit State Handles Open

area/transport enhancement P1

Difficulty 5/5 Over a week Newbie friendliness 25/100

modelcontextprotocol/java-sdk#1010 · Opened Jun 6, 2026
SEP-2468: Recommend Issuer (iss) Parameter in MCP Auth Responses Open

area/authorization enhancement P1 ready for work

modelcontextprotocol/java-sdk#1008 · 1 comment · 1 assignee · Opened Jun 6, 2026
SEP-2549: TTL for List Results Open

area/mcp-schema enhancement P1 ready for work

Difficulty 4/5 3-5 days Newbie friendliness 35/100

modelcontextprotocol/java-sdk#1009 · 1 comment · Opened Jun 6, 2026
SEP-2352: Clarify authorization server binding and migration Open

area/authorization enhancement P1 ready for work

Difficulty 4/5 3-5 days Newbie friendliness 35/100

modelcontextprotocol/java-sdk#1007 · 1 comment · Opened Jun 6, 2026
SEP-2322: Multi Round-Trip Requests Open

area/mcp-schema area/transport enhancement P1

Difficulty 5/5 Over a week Newbie friendliness 35/100

modelcontextprotocol/java-sdk#1004 · 1 comment · Opened Jun 6, 2026
SEP-2260: Require Server requests to be associated with a Client request Open

area/client enhancement P1

Difficulty 4/5 3-5 days Newbie friendliness 35/100

modelcontextprotocol/java-sdk#1003 · 1 comment · Opened Jun 6, 2026
SEP-2106: Tools inputSchema & outputSchema Conform to JSON Schema 2020-12 Open

enhancement

Difficulty 4/5 3-5 days Newbie friendliness 35/100

modelcontextprotocol/java-sdk#1000 · Opened Jun 6, 2026
SEP-2164: Standardize resource not found error code (-32602) Open

area/server enhancement P1 ready for work

modelcontextprotocol/java-sdk#1001 · 1 assignee · Opened Jun 6, 2026
SEP-1865: MCP Apps - Interactive User Interfaces for MCP Open

enhancement extensions P2

Difficulty 5/5 Over a week Newbie friendliness 30/100

modelcontextprotocol/java-sdk#999 · 1 comment · Opened Jun 6, 2026
SEP-2243: HTTP Header Standardization for Streamable HTTP Transport Open

area/server area/transport enhancement P1

Difficulty 3/5 1-2 days Newbie friendliness 68/100

modelcontextprotocol/java-sdk#990 · 3 comments · Opened May 29, 2026
Server should handle paginated requests Open

area/server enhancement P3

Difficulty 4/5 3-5 days Newbie friendliness 52/100

modelcontextprotocol/java-sdk#967 · 3 comments · Opened May 17, 2026
Streamable HTTP server accepts POST requests with non-JSON request Content-Type Open

enhancement needs confirmation P3

Difficulty 3/5 1-2 days Newbie friendliness 65/100

modelcontextprotocol/java-sdk#961 · Opened May 15, 2026
StdioClientTransport does not propagate unexpected child process exit during initialization Open

area/transport bug P2

Difficulty 3/5 1-2 days Newbie friendliness 55/100

modelcontextprotocol/java-sdk#959 · 1 comment · Opened May 14, 2026
Streamable HTTP accepts unsupported or malformed MCP-Protocol-Version headers Open

bug P2

Difficulty 3/5 1-2 days Newbie friendliness 68/100

modelcontextprotocol/java-sdk#957 · Opened May 13, 2026
Servlet transports serialize McpError exceptions instead of JSON-RPC error envelopes Open

bug P2 ready for work

Difficulty 3/5 1-2 days Newbie friendliness 68/100

modelcontextprotocol/java-sdk#955 · 3 comments · Opened May 12, 2026
`HttpServletStreamableServerTransportProvider` removes session on non-fatal failure Open

bug P2 ready for work

Difficulty 3/5 1-2 days Newbie friendliness 72/100

modelcontextprotocol/java-sdk#952 · 3 comments · Opened May 10, 2026
Add Bulk Operations for tools Open

enhancement P3 ready for work

Difficulty 3/5 1-2 days Newbie friendliness 48/100

modelcontextprotocol/java-sdk#941 · 1 comment · Opened Apr 29, 2026
set loggingConsumer after client initialization Open

waiting for triage

Difficulty 3/5 1-2 days Newbie friendliness 58/100

modelcontextprotocol/java-sdk#938 · Opened Apr 27, 2026
StdioClientTransport should support bounded child process termination Open

enhancement P2 ready for work

Difficulty 4/5 3-5 days Newbie friendliness 55/100

modelcontextprotocol/java-sdk#937 · 4 comments · Opened Apr 25, 2026
StdioServerTransportProvider should support a stdin-close callback without interrupting shutdown Open

waiting for triage

Difficulty 4/5 3-5 days Newbie friendliness 68/100

modelcontextprotocol/java-sdk#936 · 2 reactions · Opened Apr 25, 2026
More extensible CallToolRequest Open

waiting for triage

Difficulty 5/5 Over a week Newbie friendliness 35/100

modelcontextprotocol/java-sdk#910 · Opened Apr 8, 2026
Stabilize flaky test: McpCompletionTests.testCompletionErrorOnMissingContext Open

needs repro P3 tests

Difficulty 4/5 3-5 days Newbie friendliness 45/100

modelcontextprotocol/java-sdk#902 · 14 comments · Opened Apr 4, 2026
StdioClientTransport missing explicit UTF-8 charset in InputStreamReader (same issue as #295, but on client side) Open

bug P2 ready for work

Difficulty 2/5 1-3 hours Newbie friendliness 74/100

modelcontextprotocol/java-sdk#898 · 1 comment · Opened Apr 2, 2026
Streamable HTTP GET after initialize sends latest MCP-Protocol-Version instead of negotiated version Open

waiting for user

Difficulty 3/5 1-2 days Newbie friendliness 76/100

modelcontextprotocol/java-sdk#883 · 2 comments · Opened Mar 27, 2026
JAVA SDK connectto streamablehttptransport raise "Client failed to initialize by explicit API call" Open

needs repro

Difficulty 4/5 3-5 days Newbie friendliness 45/100

modelcontextprotocol/java-sdk#882 · 1 reaction · Opened Mar 25, 2026
Servlet-based server transports read request body with wrong charset encoding Open

bug P2 ready for work

Difficulty 3/5 1-2 days Newbie friendliness 64/100

modelcontextprotocol/java-sdk#880 · Opened Mar 23, 2026
Allow subclasses to be used to customize server behavior Open

waiting for triage

Difficulty 5/5 Over a week Newbie friendliness 35/100

modelcontextprotocol/java-sdk#872 · Opened Mar 17, 2026
Servlet transports block Tomcat thread Open

needs confirmation

Difficulty 4/5 3-5 days Newbie friendliness 48/100

modelcontextprotocol/java-sdk#859 · 1 comment · 1 reaction · Opened Mar 7, 2026
API: Generalize client notification handlers for SDK client classes Open

waiting for triage

Difficulty 5/5 Over a week Newbie friendliness 35/100

modelcontextprotocol/java-sdk#858 · Opened Mar 6, 2026
Support application/json responses in Streamable HTTP transport (opt-in JSON response mode) Open

enhancement P2

Difficulty 4/5 3-5 days Newbie friendliness 64/100

modelcontextprotocol/java-sdk#844 · 11 comments · Opened Mar 4, 2026

modelcontextprotocol/java-sdk

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