evalLABSCO SUMMARY
A calculator that speaks a real expression language.
The whole surface is one call, and that is the point: an assistant needing a number, a sorted list or a filtered array gets a deterministic answer instead of an estimate. The engine's syntax is the ceiling — whatever expr-lang can express works, and there is no way to reach outside the expression.
What it is
An MCP server that hands one job to the expr-lang engine: evaluate an expression and return the result. It exists so an assistant can do data manipulation exactly rather than talk its way through it — sorting a list of records, filtering an array, computing a number.
What you get
- Evaluate any expr-lang expression and get the result back —
eval - Arithmetic including modulo and exponentiation, string concatenation, length and case conversion, and boolean and comparison operators
- Array work — mapping, filtering, reducing and sorting — over structures you pass in, for example
sortBy(users, .Age, "desc") - Conditional logic, ternaries, and the engine's built-in mathematical, string, array and date functions
Requirements
Go 1.18 or higher to build: clone the repository, go mod download, then go build -o bin/server (go build -o bin/server.exe on Windows). Point the client config at that binary — the documented entry names the server eval. No account, no key, nothing reached over the network.
Setup effort
Build from source — git clone https://github.com/ivan-saorin/mcp-expr-lang.git
USE CASES
01
Sorting records mid-conversation
Pass an array of objects and an expression that orders them by a field, and get the sorted list back.
02
Doing arithmetic exactly
Hand the calculation to the engine rather than having the model perform it in prose.
03
Filtering a list down to what matters
Express the condition once and get only the matching entries back.
1 tool
Listed in project docs. Your client may show a different list.
BEFORE YOU INSTALL
What to know first
Tools you get
1 tool named in the project's documentation.
Requires
Go 1.18 or later
Where it runs
The documented client runs the server on your machine.
INSTALLATION
Connect your client
You clone and build this one yourself.
Server setup
TERMINAL
git clone https://github.com/ivan-saorin/mcp-expr-lang.git
cd mcp-expr-lang
go mod download
go build -o bin/server
chmod +x bin/serverMCP Clients
Any MCP client
ANY MCP CLIENT · JSON
{
"mcpServers": {
"eval": {
"command": "<YOUR_PATH_TO_MCP_EXPR_LANG>/bin/server"
}
}
}
