MCP server LiquidJava

LiquidJava MCP

A Java MCP server that exposes LiquidJava verification tools to LLM agents over stdio.

It allows agents to run the LiquidJava verification, retrieve structured diagnostics, inspect the verification context, and query LiquidJava's solver with custom assumptions and conclusions. It also comes with a skill that guides agents on how and when to use the MCP tools.

Installation

Build the project with mvn package and then point your MCP client at the resulting jar:

{
  "servers": {
    "liquidjava-mcp": {
      "type": "stdio",
      "command": "java",
      "args": [
        "-jar",
        "/path/to/liquidjava-mcp/target/liquidjava-mcp.jar"
      ]
    }
  }
}

Tools

Overview

Tool	Purpose	Input	Output
verify	Run the verification and get human-readable output (same as the CLI)	path, debug?	standard LiquidJava output
get_diagnostics	Run the verification and get more detailed structured diagnostics	path	errors and warnings arrays (type, severity, location, message, refinements, hints, counterexamples)
get_locals	Inspect verification context (variables in scope) at a specific source position	path, file?, line, column	variables (name, internal name, type, refinement, location)
get_globals	Inspect global definitions (aliases, ghosts, states) available in the program	path, file?	aliases, ghosts, states
get_contracts	Inspect method and constructor contracts	path, className?, signature?	contracts (qualified signature, parameters, return refinement, state transitions, location)
get_state_machine	Parse a Java file's LiquidJava typestate protocol	path	stateMachine with states and transitions
check_validity	Check if assumptions imply a conclusion via the solver	variables, ghosts, assumptions, conclusion	status (valid, invalid, or unknown), counterexample (for invalid results)
check_satisfiability	Check if constraints are satisfiable via the solver	variables, ghosts, constraints	status (sat, unsat, or unknown), assignment (for satisfiable results)

The verify, get_diagnostics, get_locals, get_globals, and get_contracts tools reuse cached analysis when the input path, source hash, and debug option match. Requests time out after 60 seconds, including time waiting for another analysis, and return a verifier error with any captured output.

verify

Runs the LiquidJava verification and returns the same output normally shown to developers. Allows agents to inspect verification conditions, their simplifications, and solver results using the debug flag.

Input: File or directory path, with optional debug flag.

Output: Verification status and the standard LiquidJava verification output.

{
  "path": ".../Example.java",
  "debug": false
}

{
  "success": false,
  "output": "Running LiquidJava on: .../Example.java\n\nRefinement Error: input >= 0 && #ret¹ == input is not a subtype of #ret¹ > 0\n..."
}

get_diagnostics

Runs the LiquidJava verification and exposes diagnostics in a machine-readable format, avoiding the need for agents to parse terminal output.

Input: File or directory path.

Output: Verification status and errors and warnings arrays of structured diagnostics, including type, severity, location, message, refinements, VCs, details, hints, and counterexamples when available.

{
  "path": ".../Example.java"
}

{
  "success": false,
  "errors": [
    {
      "refinements": {
        "expected": "#ret_1 > 0",
        "found": "input >= 0 && #ret_1 == input"
      },
      "vc": {
        "expected": "#ret_1 > 0",
        "found": "∀input:int, input >= 0 => \n∀#ret_1:int, #ret_1 == input",
        "history": [
          {
            "implication": "∀input:int, input >= 0 => \n∀#value_0:int, #value_0 == input => \n∀#ret_1:int, #ret_1 == #value_0"
          },
          {
            "implication": "∀input:int, input >= 0 => \n∀#ret_1:int, #ret_1 == input",
            "simplification": "Substitution"
          }
        ]
      },
      "type": "RefinementError",
      "severity": "error",
      "counterexample": [
        {"variable": "input", "value": "0"},
        {"variable": "#ret_1", "value": "0"}
      ],
      "declarationLocation": {
        "file": ".../Example.java",
        "startColumn": 9,
        "endLine": 14,
        "endColumn": 5,
        "startLine": 11
      },
      "location": {
        "file": ".../Example.java",
        "startColumn": 9,
        "endLine": 13,
        "endColumn": 21,
        "startLine": 13
      },
      "message": "input >= 0 && #ret¹ == input is not a subtype of #ret¹ > 0"
    }
  ],
  "warnings": []
}

get_locals

Exposes the verification context available at a specific point in the program.

Input: A path to the Java source file or directory to verify, plus line and column identifying the source position to inspect. An optional file parameter specifies a different file for filtering variables. When omitted, path is used instead. Lines and columns are one-based.

Output: variables. Each variable includes its source name, verifier internalName, Java type, refinement predicate, and source location (inclusive ends). Entries include declarations and refinement instances recorded before the position in enclosing scopes. Internal names preserve relationships between predicates. Positions outside recorded scopes return an empty array. This exposes source-filtered verifier history; synthesized branch-merge instances can carry the original declaration location, so it does not reconstruct the exact solver state at the cursor.

{
  "path": ".../Example.java",
  "line": 13,
  "column": 20
}

{
  "variables": [
    {
      "name": "input",
      "internalName": "input",
      "location": {
        "file": ".../Example.java",
        "startColumn": 41,
        "endLine": 11,
        "endColumn": 45,
        "startLine": 11
      },
      "type": "int",
      "refinement": "input >= 0"
    },
    {
      "name": "value",
      "internalName": "#value_0",
      "location": {
        "file": ".../Example.java",
        "startColumn": 13,
        "endLine": 12,
        "endColumn": 26,
        "startLine": 12
      },
      "type": "int",
      "refinement": "#value_0 == input"
    },
    {
      "name": "value",
      "internalName": "value",
      "location": {
        "file": ".../Example.java",
        "startColumn": 13,
        "endLine": 12,
        "endColumn": 26,
        "startLine": 12
      },
      "type": "int",
      "refinement": "true"
    },
    {
      "name": "ret",
      "internalName": "#ret_1",
      "location": {
        "file": ".../Example.java",
        "startColumn": 9,
        "endLine": 13,
        "endColumn": 21,
        "startLine": 13
      },
      "type": "int",
      "refinement": "#ret_1 == #value_0"
    },
    {
      "name": "this#Example",
      "internalName": "this#Example",
      "location": {
        "file": ".../Example.java",
        "startColumn": 9,
        "endLine": 13,
        "endColumn": 21,
        "startLine": 13
      },
      "type": "com.example.Example",
      "refinement": "true"
    }
  ]
}

get_globals

Provides global definitions available in the program.

Input: A path to the Java source file or directory to verify, optionally with a file identifying which source file's ghosts and states to return.

Output: aliases, ghosts, and states. Aliases include parameter names, parameter types, and predicates; ghosts and states include qualified names, return types, parameter types, and their defining refinements when available.

{
  "path": ".../Example.java"
}

{
  "aliases": [
    {
      "predicate": "v >= 0",
      "parameterTypes": ["int"],
      "parameters": ["v"],
      "name": "Positive"
    }
  ],
  "ghosts": [
    {
      "qualifiedName": "com.example.Example.size",
      "file": ".../Example.java",
      "name": "size",
      "parameterTypes": ["com.example.Example"],
      "returnType": "int"
    }
  ],
  "states": [
    {
      "qualifiedName": "com.example.Example.closed",
      "refinement": "state1(_) == 1",
      "file": ".../Example.java",
      "parameterTypes": ["com.example.Example"],
      "returnType": "boolean",
      "name": "closed"
    },
    {
      "qualifiedName": "com.example.Example.open",
      "refinement": "state1(_) == 0",
      "file": ".../Example.java",
      "parameterTypes": ["com.example.Example"],
      "returnType": "boolean",
      "name": "open"
    }
  ]
}

get_contracts

Returns the method and constructor contracts registered during verification. This includes source contracts and external refinement contracts.

Input: A path to the Java source file or directory to verify. className optionally filters by an exact qualified target class name. signature optionally filters by an exact complete qualified method or constructor signature, including parameter types.

Output: Each contract includes its target class, signature, return type and refinement, refined parameters, paired state transitions, and declaration location.

{
  "path": ".../Example.java",
  "className": "com.example.Example",
  "signature": "com.example.Example.requirePositive(int)"
}

{
  "contracts": [
    {
      "className": "com.example.Example",
      "signature": "com.example.Example.requirePositive(int)",
      "returnType": "void",
      "parameters": [
        {"name": "input", "type": "int", "refinement": "input > 0"}
      ],
      "returnRefinement": "true",
      "stateTransitions": [],
      "location": {
        "file": ".../Example.java",
        "startLine": 10,
        "startColumn": 5,
        "endLine": 11,
        "endColumn": 6
      }
    }
  ]
}

get_state_machine

Parses a Java source file and returns the LiquidJava typestate protocol declared by its @StateSet and @StateRefinement annotations. The result describes the possible states, initial states, and method transitions. A transition's fromCondition and toCondition contain any non-state conditions such as cond ? state1 : state2 or cond && state1.

Input: path, an existing Java source file. Directories are not accepted because the parser returns the state machine for one source file at a time.

Output: An object containing a stateMachine value with the qualified class name, states, initial transitions, and method transitions. stateMachine is null when the file does not declare a state machine.

{
  "path": ".../File.java"
}

{
  "stateMachine": {
    "className": "example.File",
    "states": [
      "open",
      "closed"
    ],
    "transitions": [
      {
        "from": "open",
        "to": "closed",
        "label": "close",
        "fromCondition": null,
        "toCondition": null
      },
      {
        "from": "open",
        "to": "open",
        "label": "read",
        "fromCondition": null,
        "toCondition": null
      }
    ],
    "initialTransitions": [
      {
        "to": "open",
        "toCondition": null
      }
    ]
  }
}

check_validity

Checks whether custom assumptions imply one conclusion using LiquidJava's solver, without verifying Java files. Declared ghost functions are translated as LiquidJava uninterpreted functions. Aliases, source constants, and implicit receiver/return/old-state bindings are not supported.

Input: variables (map of names to primitive or reference types), ghosts (map of names to uninterpreted function declarations with parameter types and a return type), assumptions (array of boolean predicate strings), and conclusion (boolean predicate string).

Output: status (valid, invalid, or unknown). Invalid results include a counterexample.

{
  "variables": {"x": "int"},
  "ghosts": {},
  "assumptions": ["x >= 0"],
  "conclusion": "x > 0"
}

{
  "status": "invalid",
  "counterexample": [{"variable": "x", "value": "0"}]
}

check_satisfiability

Checks whether custom constraints have a satisfying assignment using LiquidJava's solver. It returns sat, unsat, or unknown; sat results include the solver's assignment when available.

Input: variables (map of names to primitive or reference types), ghosts (map of names to uninterpreted function declarations with parameter types and a return type), and constraints (array of boolean predicate strings).

Output: status (sat, unsat, or unknown). Satisfiable results include an assignment.

{
  "variables": {"x": "int"},
  "ghosts": {},
  "constraints": ["x > 0", "x < 2"]
}

{
  "status": "sat",
  "assignment": [{"variable": "x", "value": "1"}]
}