MCP Server (LLM Integration)

Giac.jl can expose its computer-algebra engine to MCP-aware LLM clients (Claude Desktop, Claude Code, Cursor, and others) through the Model Context Protocol. The integration is implemented as a weak-dependency package extension: users who do not need MCP see no behavior change, no new dependency in their manifest, and no precompilation cost.

Installation

using Pkg
Pkg.add("ModelContextProtocol")

Giac.jl itself does NOT pull ModelContextProtocol.jl in transitively. You install it explicitly when (and only when) you want the MCP server.

Quickstart

using Giac, ModelContextProtocol

server = giac_mcp_server()   # construct the server (no I/O yet)
start!(server)                # blocks on STDIO transport

start! reads JSON-RPC requests from stdin, writes responses to stdout, and logs to stderr. Press Ctrl-C to stop.

What tools are exposed

The returned Server advertises two MCP tools:

• giac_eval — evaluate any Giac/Xcas expression. Input: expr (string). Output: the textual result of the expression.

  expr = "factor(x^4-1)"   →   (x-1)*(x+1)*(x^2+1)
  expr = "laplace(exp(-t),t,s)"   →   1/(s+1)

  Multiple statements separated by ; are allowed; the response is the value of the last statement. Each tool call is independent — variable bindings (a := 5) do NOT persist across calls.

• giac_search — search the Giac command catalogue by keyword. Input: query (string). Output: comma-separated list of matching command names, or the literal "No commands matched." when nothing matches.

  The search first tries prefix matching (the canonical Giac.jl behavior) and falls back to substring matching so LLM-style queries like "matrix" or "prime" find the relevant commands.

Setup with Claude Desktop

Edit ~/.config/claude/claude_desktop_config.json (or the platform equivalent) and add a mcpServers entry:

{
  "mcpServers": {
    "giac-cas": {
      "command": "julia",
      "args": [
        "--project=/path/to/env",
        "-e",
        "using Giac, ModelContextProtocol; start!(giac_mcp_server())"
      ]
    }
  }
}

Substitute /path/to/env with a Julia environment that has both Giac and ModelContextProtocol installed. A dedicated environment (for example ~/.julia/environments/mcp-giac/) is recommended so the MCP server starts as quickly as Julia allows. Restart Claude Desktop after editing the config.

Setup with Claude Code

claude mcp add-json "giac-cas" '{"command":"julia","args":["--project=/path/to/env","-e","using Giac, ModelContextProtocol; start!(giac_mcp_server())"]}'

Confirm with claude mcp list. From any Claude Code session, ask:

Use the Giac MCP server to factor x^4 - 1.

and Claude will call the giac_eval tool and return the Giac-computed factorization.

Setup with other MCP clients (Cursor, ...)

The command is the same — only the configuration UI differs. Most clients accept a JSON object with a command and args array; copy the structure from the Claude Desktop section.

Manual JSON-RPC test

To verify the server end-to-end without an LLM client:

printf '%s\n%s\n' \
  '{"jsonrpc":"2.0","method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}},"id":1}' \
  '{"jsonrpc":"2.0","method":"tools/call","params":{"name":"giac_eval","arguments":{"expr":"factor(x^4-1)"}},"id":2}' \
| julia --project -e 'using Giac, ModelContextProtocol; start!(giac_mcp_server())' \
  2>/dev/null | jq .

The output is two JSON-RPC response objects: the initialize reply and the tools/call reply whose content[0].text contains Giac's factored form of x^4 - 1.

Example prompts

Once the server is wired into your MCP client, you can address it in plain natural language. The LLM routes the request to giac_eval (or giac_search) and returns Giac's exact symbolic result. A few prompts to get started, grouped by domain:

French — direct style

• factorise avec giac x²-1
• développe avec giac (a+b)²
• résous avec giac x² - 5x + 6 = 0
• dérive avec giac sin(x²)
• intègre avec giac x·exp(x)
• calcule avec giac la limite de sin(x)/x en 0
• décompose avec giac 1/(x³-1) en éléments simples

English — direct style

• with giac, factor x^4 - 1
• with giac, expand (x+y+z)^3
• with giac, solve x^3 - 6x^2 + 11x - 6 = 0
• with giac, integrate 1/(x^2 + 2x + 5) dx
• with giac, compute the Laplace transform of t^2 * exp(-t) * sin(t)
• with giac, compute the Z-transform of n^2

English — natural, story-style

These read like questions a human would actually ask. The LLM still routes them through giac_eval, but the framing exercises its judgement about which Giac construct to invoke.

• with giac, I'm stuck on x^4 - 5x^2 + 4 — can you break it into factors?
• with giac, between which two integers does the real root of x^3 + x - 1 = 0 lie?
• with giac, what's the slope of tan(x^2) at x = 1?
• with giac, give me the area under the bell curve exp(-x^2) over the whole real line
• with giac, does the sequence (1 + 1/n)^n converge, and to what?
• with giac, a mass on a spring satisfies y'' + 4y = cos(2t) — find the motion
• with giac, a population grows logistically with y' = y(1-y) and starts at 1/2; what's y(t)?
• with giac, is the matrix [[1,2,3],[4,5,6],[7,8,10]] invertible? Prove it
• with giac, the matrix [[2,1,0],[0,2,1],[0,0,2]] isn't diagonalizable — what's its Jordan structure?
• with giac, what polynomial of degree 3 passes through (0,1), (1,2), (2,5), (3,10)?
• with giac, do x^2 + x + 1 and x^3 - 1 share a common root?
• with giac, my password is the prime just after one billion — what is it?
• with giac, is the Mersenne number 2^31 - 1 actually prime?
• with giac, find integers u and v such that 1071·u + 462·v = gcd(1071, 462)
• with giac, an engineer needs the Laplace transform of t² e^(-t) sin(t) — deliver it
• with giac, recover the time-domain signal whose Laplace transform is (s+1)/((s²+1)(s+2))
• with giac, rewrite sin(5x) using only sin(x) and cos(x)
• with giac, fuse sin(x) + cos(x) into a single sinusoid
• with giac, how many 5-card poker hands are there from a standard deck?
• with giac, give me the 50th Fibonacci number
• with giac, fit a line through (1,2), (2,5), (3,7), (4,10) and tell me the slope
• with giac, Euler famously summed 1/k² — confirm his answer
• with giac, give me a closed-form expression for 1³ + 2³ + … + n³
• with giac, does the alternating sum (-1)^k / k converge, and to what value?

Catalogue search

Use the giac_search tool when you don't remember the exact command name:

• with giac, which commands deal with matrices?
• with giac, what's available for prime numbers?
• with giac, list the Laplace-related commands

API reference

giac_mcp_server(; name="giac-cas", version=string(pkgversion(Giac)), kwargs...) -> ModelContextProtocol.Server

using Pkg; Pkg.add("ModelContextProtocol")
using Giac, ModelContextProtocol
start!(giac_mcp_server())   # blocks on STDIO transport

Limitations and future work

The first release is intentionally minimal. Deferred to later iterations:

• MCP Resources that expose Giac documentation by domain so the LLM can fetch reference material on demand.
• MCP Prompts offering pre-built templates such as "solve step by step, verify each step with giac_eval".
• A structured invocation tool accepting {"command": "factor", "args": ["x^4-1"]} for callers that want typed arguments instead of free-form expressions.
• Session/context state across tool calls (e.g., a := 5 persisting). Each tool call is currently independent.
• A PackageCompiler.jl sysimage to reduce Julia's startup latency when an LLM client launches the server as a subprocess.