The-40-Thieves/codecalc

**codecalc is an offline, self-hosted MCP server that gives an AI agent a
calculator, a code runner, and a logic checker — so it gets a *correct* answer
instead of a guessed one.** It runs code in **31 languages**, does exact
symbolic math, solves SMT/logic problems, and measures complexity, all exposed
as **51 MCP tools**.
**Fastest path:** uvx 'codecalc[full]' setup --write registers codecalc with your MCP client automatically. New to MCP, or want more detail first? See QUICKSTART.md, or the Install section below.
Three things nobody else offers together cleanly:
- **Offline-core** — ships no model, no API key, no gateway, no telemetry.
The core opens no sockets; network access is opt-in and only where a
specific tool's job needs it (the Piston provider, install_package, the
runtime-update tools, executed code unless no_net, and a one-time
in-process grammar download on first analyze_complexity — full breakdown
in the network-boundary table below).
- **Safe execution of untrusted code** — an opt-in *strict* isolation
boundary (gVisor+Docker on Linux, AppContainer on Windows) layered above
the default rlimit sandbox, fail-closed and attested.
- **Verification tools** — verify_translation proves a port to another
language behaves identically, verify_optimization proves an optimization
preserved behavior, and z3_check proves or refutes logic with an SMT
solver.
When to use codecalc
Use it when you want a free, local, private, hardened code-runner and
verifier that an MCP agent can call directly — no vendor account, no cloud
spend, nothing leaving the machine except where a tool's job explicitly
requires it.
Reach for something else when you want managed cloud scale instead of
self-hosting (a hosted sandbox like E2B or Modal), or when you're not
self-hosting at all and the model vendor's built-in code interpreter already
covers what you need.
codecalc vs. the alternatives
codecalc is not a general cloud sandbox and not a vendor code interpreter. It
overlaps with several things and beats them in only one narrow place — forcing a
model to *measure* a claim instead of asserting it. Where that isn't what you
need, one of these is the better tool, and this table says so plainly.
| You want… | Better fit | Why |
|---|---|---|
| To just run some Python/JS quickly, zero setup | Your model vendor's built-in interpreter | Already there, already sandboxed, nothing to install. Anthropic's code-execution tool has internet access "completely disabled" and cannot install packages at runtime; OpenAI's hosted containers have no outbound network access by default, with an org-level network_policy allowlist as an opt-in. Both return output artifacts by reference (Anthropic a file_id via the Files API, OpenAI a container_file_citation) rather than inline (Anthropic code-execution tool docs, https://platform.claude.com/docs/en/agents-and-tools/tool-use/code-execution-tool; OpenAI shell/container tool guide, https://developers.openai.com/api/docs/guides/tools-shell; both retrieved 2026-09-07) |
| Heavy or multi-tenant workloads, managed scale | A cloud sandbox (E2B, Modal, Daytona) | Per-tenant Firecracker/gVisor isolation codecalc does not claim by default |
| Pure arithmetic or symbolic math, nothing else | A small calculator or SymPy MCP | Lower token cost; none of the 31-language runtime machinery |
| **A model to stop _guessing_ numbers, equivalence, and speedups — locally, privately, with graded evidence** | **codecalc** | Exact rationals, verify_translation/verify_optimization, and unenforced/grade honesty — offline, no account |
**Do not reach for codecalc if** you need multi-tenant or network-exposed
isolation (its threat model is explicitly single-operator, local, stdio), if
zero-setup convenience matters more than measurement, or if a hosted interpreter
already covers your case. It earns its keep only when the *correctness of the
claim* — not just "it ran" — is the point.
Install
Quickstart with codecalc setup
The fastest path to a working MCP connection, without reading the rest of
this section:
It detects which MCP client is installed (Claude Desktop, Claude Code,
Cursor, VS Code, Zed — pass --client=NAME if none or several are found),
reuses codecalc doctor's own backend/extras/grammar-cache checks, prints the
exact config block in that client's own JSON shape with absolute paths
already filled in, runs two real canaries (execute_code, evaluate_expression)
to prove the connection would work, and ends in one verdict: ready /
degraded / not-ready. --write is the only mode that changes anything —
it MERGES the codecalc entry into your existing client config (every other