@cyanheads/calculator-mcp-server
Evaluate, simplify, and differentiate mathematical expressions via MCP. STDIO or Streamable HTTP.
1 Tool • 1 Resource
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**Public Hosted Server:** [https://calculator.caseyjhand.com/mcp](https://calculator.caseyjhand.com/mcp)
---
## Overview
Calculator powered by math.js. Verify numeric results, simplify algebraic expressions, and compute symbolic derivatives through one tool. Runs as a stdio process, a local Streamable HTTP server, or the public hosted endpoint above.
### Tools
| Tool | Description |
|:----------|:------------|
| `calculate` | Evaluate math expressions, simplify algebraic expressions, or compute symbolic derivatives. |
### Resources
| Resource | Description |
|:------------|:------------|
| `calculator://help` | Available functions, operators, constants, and syntax reference. |
## Capability reference
### `calculate` tool
- One `expression` per call. `operation` selects `evaluate` (default), `simplify`, or `derivative`; derivatives require `variable` (e.g. `"x"`).
- Evaluate arithmetic, trigonometry, logarithms, statistics, matrices, complex numbers, units, and combinatorics; assign numeric variables through `scope`, e.g. `{ "x": 5 }`.
- `numericType` selects `number`, `BigNumber` (64 significant digits, for values that overflow a 64-bit float), or `Fraction` (exact rationals). Fraction mode returns `fraction_unsupported`, with guidance to change numeric type, when a result has no exact rational value (`sqrt(2)`), the expression calls a function Fraction mode cannot compute (`sqrt(4)`, `5!`), or it uses a value Fraction mode holds only as a rounded float (`pi`, `2^(1/2)`).
- `precision` sets 1–16 significant digits for numeric results. Blank optional `variable` and `precision` values are treated as omitted; scope and precision do not affect symbolic operations.
- Simplification includes algebraic and trigonometric identities (`2x + 3x` → `5 * x`); `unchanged: true` identifies expressions the simplifier cannot reduce, including polynomial factoring and rational cancellation cases.
- Returns the result string, result type, original expression, and operation. Validation failures include typed reasons and recovery hints.
---
### `calculator://help` resource
- Markdown reference for functions, operators, constants, units, and expression syntax; no parameters.
- Examples cover scope, matrices, complex numbers, precision, and all three operations.
- Cacheable for 24 hours with public scope (`cacheHint`) — static content that never changes at runtime.
## Features
Built on [`@cyanheads/mcp-ts-core`](https://github.com/cyanheads/mcp-ts-core): stdio and Streamable HTTP transports, pluggable auth (`none` / `jwt` / `oauth`), swappable storage (`in-memory`, `filesystem`, `Supabase`, `Cloudflare KV/R2/D1`), structured logging with optional OpenTelemetry tracing.
Calculator-specific:
- Hardened math.js v15 instance — dangerous functions disabled, evaluation run under a `vm` timeout
- No auth required — all operations are read-only and stateless
- Input validation: expression length limits and rejection of multiple statements; matrix row separators and string contents remain valid
- Result validation: blocked result types (functions, parsers, result sets), configurable max result size
- Size limits: functions that build a matrix or string from a size, product, broadcast, index, or precision argument are capped per call, and each evaluation has a total element budget; oversized requests fail fast with `result_too_large`
- Scope sanitization: numeric-only values, prototype pollution prevention (blocked `__proto__`, `constructor`, etc.)
Agent-friendly output:
- Effective-call echo — every response echoes the expression and operation, plus which scope variables and what precision were applied, so agents can verify what was actually computed
- Discriminated output contracts — `unchanged: true` on `simplify` flags a no-op result instead of silently returning the same expression
- Typed error reasons — validation and evaluation failures carry a typed `reason` (e.g. `fraction_unsupported`, `evaluation_timeout`, `disallowed_result_type`) plus an actionable recovery hint, rather than a raw exception
## Getting started
### Public Hosted Instance
A public instance is available at `https://calculator.caseyjhand.com/mcp` — no installation required. Point any MCP client at it via Streamable HTTP:
```json
{
"mcpServers": {
"calculator-mcp-server": {
"type": "streamable-http",
"url": "https://calculator.caseyjhand.com/mcp"
}
}
}
```
### Self-Hosted / Local
Add one of the following to your MCP client configuration file:
```json
{
"mcpServers": {
"calculator-mcp-server": {
"type": "stdio",
"command": "bunx",
"args": ["@cyanheads/calculator-mcp-server@latest"],
"env": {
"MCP_TRANSPORT_TYPE": "stdio",
"MCP_LOG_LEVEL": "info"
}
}
}
}
```
Or with npx (no Bun required):
```json
{
"mcpServers": {
"calculator-mcp-server": {
"type": "stdio",
"command": "npx",
"args": ["-y", "@cyanheads/calculator-mcp-server@latest"],
"env": {
"MCP_TRANSPORT_TYPE": "stdio",
"MCP_LOG_LEVEL": "info"
}
}
}
}
```
Or with Docker:
```json
{
"mcpServers": {
"calculator-mcp-server": {
"type": "stdio",
"command": "docker",
"args": [
"run", "-i", "--rm",
"-e", "MCP_TRANSPORT_TYPE=stdio",
"ghcr.io/cyanheads/calculator-mcp-server:latest"
]
}
}
}
```
For Streamable HTTP, set the transport and start the built server:
```sh
MCP_HTTP_PORT=3010 bun run start:http
# Server listens at http://localhost:3010/mcp
```
### Prerequisites
- [Bun v1.4.0](https://bun.sh/) or higher
### Installation
1. **Clone the repository:**
```sh
git clone https://github.com/cyanheads/calculator-mcp-server.git
```
2. **Navigate into the directory:**
```sh
cd calculator-mcp-server
```
3. **Install dependencies:**
```sh
bun install
```
## Configuration
| Variable | Description | Default |
|:---------|:------------|:--------|
| `CALC_MAX_EXPRESSION_LENGTH` | Maximum allowed expression string length (10–10,000). | `1000` |
| `CALC_EVALUATION_TIMEOUT_MS` | Maximum evaluation time in milliseconds (100–30,000). | `5000` |
| `CALC_MAX_RESULT_LENGTH` | Maximum result string length in characters (1,000–1,000,000). | `100000` |
| `MCP_TRANSPORT_TYPE` | Transport: `stdio` or `http`. | `stdio` |
| `MCP_HTTP_HOST` | Hostname for the HTTP server. | `127.0.0.1` |
| `MCP_HTTP_PORT` | Port for HTTP server. | `3010` |
| `MCP_HTTP_ENDPOINT_PATH` | Path for the HTTP MCP endpoint. | `/mcp` |
| `MCP_HTTP_MAX_BODY_BYTES` | Maximum inbound HTTP request size; `0` disables the limit. | `1048576` |
| `MCP_AUTH_MODE` | Auth mode: `none`, `jwt`, or `oauth`. | `none` |
| `MCP_SESSION_MODE` | `auto`, `stateful`, or `stateless`. The server declares `stateless` in code, so every launch path resolves the same way; setting this overrides that declaration. | `stateless` |
| `MCP_LOG_LEVEL` | Log level (RFC 5424). | `info` |
See [`.env.example`](./.env.example) for optional session, resumability, logging, and telemetry settings.
## Running the server
### Local development
- **Build and run the production version:**
```sh
bun run build
bun run start:http # or start:stdio
```
- **Run checks and tests:**
```sh
bun run devcheck # Lints, formats, type-checks
bun run test # Runs test suite
```
### Docker
```sh
docker build -t calculator-mcp-server .
docker run -p 3010:3010 calculator-mcp-server
```
The image defaults to Streamable HTTP on port `3010`, stateless sessions, and logs at `/var/log/calculator-mcp-server`. OpenTelemetry dependencies are installed by default; build with `--build-arg OTEL_ENABLED=false` to omit them.
## Project structure
| Directory | Purpose |
|:----------|:--------|
| `src/mcp-server/tools/` | Tool definitions (`*.tool.ts`). |
| `src/mcp-server/resources/` | Resource definitions (`*.resource.ts`). |
| `src/services/` | Domain service integrations (MathService). |
| `src/config/` | Environment variable parsing and validation with Zod. |
| `docs/` | Generated directory tree. |
| `tests/` | Calculation, configuration, and response-contract tests. |
## Development guide
See [`AGENTS.md`](./AGENTS.md) or [`CLAUDE.md`](./CLAUDE.md) for development guidelines and architectural rules. The short version:
- Handlers throw, framework catches — no `try/catch` in tool logic
- Use `ctx.log` for logging
- Register new tools and resources in `src/index.ts`
## Contributing
Issues are welcome. Run checks before submitting:
```sh
bun run devcheck
bun run test
```
## License
Apache-2.0 — see [LICENSE](LICENSE) for details.