Cal Server

The Cal Server is a lightweight mathematical expression evaluator built on the FastMCP framework and powered by Bun. It exposes a single tool, , that accepts a string containing any valid arithmetic expression and returns the computed result. By leveraging the library, the server supports standard operators, parentheses, and a set of built‑in constants (, , , ). This design removes the need for developers to write custom parsing logic whenever they want to incorporate quick calculations into an AI workflow.

For AI assistants, the server solves a common pain point: executing arbitrary mathematical expressions on demand without exposing the entire runtime environment. Instead of sending raw code to a remote interpreter, an assistant can simply invoke with the expression string and receive a reliable numeric or boolean result. Because the service communicates via standard input/output, it can be wrapped in any MCP client—Claude Desktop, Smithery, or a custom integration—without additional networking overhead. The result is a deterministic, sandboxed computation that respects the same input validation rules enforced by Zod.

Key capabilities include:

• Expression Parsing: Handles operator precedence, parentheses, and exponentiation.
• Constant Support: Built‑in values for (Euler’s number), , and logical booleans.
• Validation: Input is strictly typed as a string, ensuring that only well‑formed expressions reach the evaluator.
• Fast Execution: Bun’s V8 engine and the minimal FastMCP stack deliver sub‑millisecond response times for simple calculations.

Typical use cases arise in data analysis pipelines, educational tools, or any scenario where an AI assistant needs to compute intermediate results on the fly. For example, a chatbot can ask a user for a budget calculation, pass the expression to , and then format the response. In a scientific context, researchers can quickly evaluate symbolic expressions or constants within a larger AI‑driven workflow.

Integrating Cal Server into an MCP‑enabled environment is straightforward: the tool name () and its single parameter () are declared in the server’s metadata, allowing AI clients to discover and invoke it automatically. Because the service runs locally in a lightweight Bun process, developers gain full control over security and resource usage while still benefiting from the convenience of an AI‑driven interface. This combination of simplicity, speed, and safety makes Cal Server a standout choice for developers who need on‑demand mathematical evaluation without the complexity of full‑featured programming runtimes.