graph-mcp-java-gen
Uses Neo4j as a versioned graph catalog backend, enabling parameterised searches for symbols and methods that ground the generation of validated, compilable Java test code.
Click on "Install Server".
Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state.
In the chat, type
@followed by the MCP server name and your instructions, e.g., "@graph-mcp-java-genWrite a Java test for the shortestPath method in the GraphTraversal class"
That's it! The server will respond to your query, and you can continue using it as needed.
Here is a step-by-step guide with screenshots.
graph-mcp-java-gen
Graph-grounded MCP server that converts natural-language requests into validated, compilable Java test methods — no hallucinated imports, no ungrounded symbols, no silent failures.
A natural-language or structured request enters an official Model Context Protocol (MCP) stdio server. A versioned graph catalog (Neo4j or JSON fixture) supplies the only symbols the generator may cite. A multi-layer validator checks syntax, framework contract, grounding, and forbidden-API rules before any source is returned. Two optional LLM agents — an intent normaliser and a post-generation reviewer — extend the pipeline to free-form input without compromising the deterministic safety envelope.
Architecture
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flowchart TD
classDef input fill:#7b2d8b,stroke:#4a1a54,color:#fff,font-size:13px
classDef mcp fill:#e07b00,stroke:#9a5700,color:#fff,font-size:13px
classDef agent fill:#1a6b8a,stroke:#0d3f52,color:#fff,font-size:13px
classDef core fill:#2d6a4f,stroke:#1b4332,color:#fff,font-size:13px
classDef graph fill:#1e3a5f,stroke:#0d1f3c,color:#fff,font-size:13px
classDef validate fill:#4a6741,stroke:#2d4026,color:#fff,font-size:13px
classDef ok fill:#155724,stroke:#0a3015,color:#fff,font-size:13px
classDef reject fill:#721c24,stroke:#3d0a0e,color:#fff,font-size:13px
NL["🌎 Free-form NL\n(generate_java_test_nlp)"]:::input
SF["📄 Structured fields\n(generate_java_test)"]:::input
TX["💬 Intent text\n(generate_java_test_from_intent)"]:::input
MCP["🔌 FastMCP stdio Server\n7 tools · zero raw Cypher"]:::mcp
A1["🤖 LLMIntentParser\nAgent 1 · gpt-4o-mini\nfield extraction"]:::agent
INT["✅ GenerationIntent\nclass · package · module\nconfig · version"]:::core
GDB["📊 Graph Catalog\nNeo4j 5.26 / JSON fixture\n8 symbols · 12 methods"]:::graph
GEN["⚙️ Template Generator\ndeterministic render"]:::core
VAL["🛡️ JavaValidator\nTree-sitter AST\ncontract · grounding\nsource-safety"]:::validate
A2["🤖 ReviewAgent\nAgent 2 · gpt-4o-mini\n6-item checklist"]:::agent
OK["✅ Accepted Java\nsource + citations\n+ review verdict"]:::ok
REJ["❌ Typed Rejection\nerror code + message\nno source returned"]:::reject
NL --> MCP
SF --> MCP
TX --> MCP
MCP -->|"NLP path"| A1
MCP -->|"direct path"| INT
A1 -->|"extracted fields"| INT
INT -->|"invalid"| REJ
INT -->|"valid"| GDB
GDB -->|"cited symbols"| GEN
GEN --> VAL
VAL -->|"any gate fails"| REJ
VAL -->|"all gates pass"| A2
A2 -->|"issues found"| REJ
A2 -->|"approved"| OKMulti-Agent Pipeline
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sequenceDiagram
autonumber
actor User
participant MCP as FastMCP Server
participant A1 as LLMIntentParser<br/>(Agent 1)
participant GDB as Graph Catalog<br/>(Neo4j / Fixture)
participant GEN as Generator +<br/>JavaValidator
participant A2 as ReviewAgent<br/>(Agent 2)
User->>MCP: generate_java_test_nlp(free-form NL)
MCP->>A1: extract intent fields
Note over A1: gpt-4o-mini · temp=0<br/>strict JSON schema
A1-->>MCP: {class, package, module, config, version}
MCP->>GDB: get versioned symbols
GDB-->>MCP: 7 cited GraphSymbol objects
MCP->>GEN: render Java + validate
Note over GEN: Tree-sitter AST<br/>contract · grounding · safety
GEN-->>MCP: validated Java source
MCP->>A2: review(source, class, package)
Note over A2: gpt-4o-mini · temp=0<br/>6-item checklist
A2-->>MCP: {approved, checklist, issues}
MCP-->>User: {status, source, citations, review}Evidence Dashboard
All measurements use independently generated CC0-licensed synthetic fixtures.
Results are from the accepted strict_graph_v2 policy on the held-out confirmation split.
Surface | Result | Artifact |
Benchmark scale | 96 CC0 intents — 32 dev / 32 val / 32 confirmation | |
Confirmation task success | 32 / 32 bounded tasks | |
Generated-source validation | 24 / 24 supported intents — syntax + contract + grounding + safety | |
Safe adversarial rejection | 8 / 8 — zero false accepts | |
Citation precision | 100% — only graph-cited symbols imported | |
Required-symbol recall | 100% — every required symbol present | |
Live Neo4j integration | Neo4j 5.26.29 — 8 symbols, 12 methods materialized | |
Official MCP benchmark | 120 / 120 expected outcomes — zero protocol errors | |
MCP warm latency (p50 / p95 / p99) | 29.13 / 48.61 / 54.23 ms at concurrency 1 | |
Java compilation | 8 / 8 class files via Eclipse ECJ 3.21 | |
External model calls (deterministic path) | 0 calls · $0.00 |
Latency figures are single-process local Windows measurements, not production SLOs.
Policy Selection
Four generation policies were evaluated. The selection objective was declared before opening the confirmation split: maximise validation task success among candidates passing all safety gates. Confirmation was opened exactly once for the selected candidate.
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xychart-beta
title "Validation: task success vs safe-rejection recall (%)"
x-axis ["no_graph_v0", "lenient_repair_v1", "strict_graph_v2 ✓", "wide_context_v3"]
y-axis "Task success (%)" 0 --> 105
bar [21.9, 75.0, 100.0, 96.9]
line [87.5, 0.0, 100.0, 87.5]Candidate | Task success | Gen valid | Safe reject | Citation prec | Decision |
| 21.9% | 0% | 87.5% | 0% | Rejected — no grounding |
| 75.0% | 100% | 0% | 100% | Rejected — 8 false accepts |
| 100% | 100% | 100% | 100% | Selected |
| 96.9% | 100% | 87.5% | 87.5% | Rejected — irrelevant context + 1 false accept |
MCP Tools
Tool | Type | Behaviour |
| Read | Returns fixture identity, provenance, license, backend, symbol count |
| Read | Parameterised name/method search; max 20 results |
| Generate | Typed fields → graph lookup → Java → all validation gates |
| Generate | Bounded 3-form grammar → same strict policy |
| Validate | Checks up to 20 000 chars; never writes or executes source |
| Multi-agent | LLM intent parser → generator → LLM reviewer; requires |
The Neo4j adapter uses fixed parameterised Cypher, rejects credentials in URIs, and refuses fixture identity collisions.
Quick Start
python -m venv .venv
# Windows
.\.venv\Scripts\Activate.ps1
# Linux / macOS
source .venv/bin/activate
pip install -r requirements-dev.txt
pip install --no-deps -e .
# Run the offline smoke test (no database needed)
python scripts/container_smoke.py python -m graph_mcp.serverMCP client configuration (VS Code / Claude Desktop)
{
"mcpServers": {
"graph-java-gen": {
"command": "/absolute/path/to/.venv/bin/python",
"args": ["-m", "graph_mcp.server"],
"cwd": "/absolute/path/to/repo"
}
}
}Enable the multi-agent NLP tool
# Add to your environment or .env file
OPENAI_API_KEY=sk-...
GRAPH_BACKEND=neo4j # optional; defaults to local JSON fixtureReproduce Evidence
# Build the CC0 benchmark fixture
python scripts/build_evaluation_fixture.py
# Run all four candidate policies and select strict_graph_v2
python scripts/evaluate_workflow.py
# Validate the claims ledger and evidence privacy rules
python scripts/validate_evidence.py
# Full test suite
pytest --cov=src --cov-report=term-missing --cov-fail-under=75
# Lint and security
ruff check src tests scripts
bandit -r src scripts -q -ll
pip-audit -r requirements.txt --progress-spinner offLive Neo4j path
# Start a local Neo4j Community instance (Docker)
docker compose up -d neo4j
python scripts/wait_for_neo4j.py
# Seed the synthetic graph fixture and verify retrieval
python scripts/seed_graph.py
python scripts/verify_neo4j.py # writes evidence/neo4j_integration.json
# Full MCP benchmark over stdio with live graph
python scripts/benchmark_mcp.py # writes evidence/mcp_benchmark.jsonJava compilation
# Requires JDK 21 on PATH
python scripts/compile_generated.py --require-compiler
# Writes evidence/java_compile.jsonSecurity Design
No raw Cypher on the MCP surface — all graph queries are parameterised.
Strict field allowlists — class names, package names, module names, versions, and config paths are checked against compiled regex patterns before any graph lookup.
Source safety scanner — generated Java is rejected if it references
Runtime.getRuntime,ProcessBuilder,System.exit,java.io,java.nio.file, orjava.net.Path traversal prevention — absolute paths and
..segments are rejected in config path fields.Grounding enforcement — every import in generated source must correspond to a symbol retrieved from the graph for that exact version.
LLM output re-validated — fields extracted by the LLM intent parser pass through the same
GenerationIntent.from_mapping()validation as direct API calls.Neo4j credentials — loaded only from environment variables; never logged or returned in evidence artifacts.
XML preflight —
defusedxmlprevents entity-expansion attacks in project-structure scanning.Container — pinned Chainguard Linux image, non-root UID/GID 65532; CI performs an MCP-over-container stdio smoke test.
See SECURITY.md for the full threat boundary.
Repository Map
src/graph_mcp/
workflow.py intent parsing · graph lookup · Java generation · validation
graph_store.py Neo4j catalog adapter (parameterised Cypher)
llm_intent_parser.py Agent 1 — LLM free-form NL → GenerationIntent
review_agent.py Agent 2 — LLM post-generation checklist reviewer
server.py FastMCP stdio server (7 tools)
evaluation.py candidate scoring and selection harness
fixtures/
synthetic_graph.json CC0 versioned framework symbol catalog (SHA-256 bound)
evaluation_cases.json 96 CC0 natural-language intents (32/32/32 split)
java_framework/ 7 independently generated Java stub classes
evidence/
claims.json machine-readable claims ledger (14 public claims)
evaluation_protocol.json pre-declared selection rules and safety gates
task_evaluation.json per-candidate, per-split, per-case results
evaluation_trace.json confirmation case-level trace
neo4j_integration.json live Neo4j integration result
mcp_benchmark.json MCP protocol benchmark (120 calls)
java_compile.json ECJ compilation result
scripts/
build_evaluation_fixture.py generate benchmark from seed
evaluate_workflow.py run and score all four candidates
validate_evidence.py verify claims ledger and privacy rules
benchmark_mcp.py official MCP stdio latency benchmark
verify_neo4j.py live graph integration check
compile_generated.py ECJ compile gate
seed_graph.py materialise fixture into Neo4j
tests/
test_generation_loop.py generation + validation unit tests
test_graph_store.py Neo4j adapter unit tests
test_mcp_protocol.py official MCP protocol conformance
test_evaluation.py evaluation harness tests
test_evidence.py claims ledger integrity tests
test_neo4j_live.py opt-in live graph tests (NEO4J_* env required)
docs/
ARCHITECTURE.md component design and data flow
POLICY_CARD.md candidate selection details
DATA_CARD.md fixture provenance and license
MCP_INTEGRATION.md client configuration guide
DEPLOYMENT.md Docker and container notes
templates/ MCP prompt templates for VS Code Copilot
examples/ sample project preflight scannerBoundaries
The following are not claimed by this repository:
Free-form intent parsing quality independent of model version — the LLM pipeline is opt-in and its results are not captured in the frozen evaluation artifacts.
Compatibility with any proprietary or confidential Java test framework.
Production latency SLO — all measurements are single-process local sequential benchmarks.
Concurrent, distributed, or high-availability operation.
Automatic execution of generated Java against hardware or a test instrument.
Any productivity, cost, yield, or test-time saving — this repository contains only generation and validation evidence.
The full machine-readable boundary is in evidence/claims.json.
License
Repository code: MIT. Graph fixture, intent cases, and Java stubs: CC0-1.0 (labelled in fixture metadata).
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