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Understanding jq Type Errors and the Plus Operator in jqlang/jq

April 11, 2026 jqlang/jq ↗

The jq programming language enforces strict type safety for the binary + operator, generating descriptive runtime errors via type_error2 in src/builtin.c whenever incompatible JSON types are combined.

The jqlang/jq repository implements the + operator as a type-aware builtin that only permits addition between compatible JSON value kinds. When operands mismatch—such as attempting to add a number to a string—the interpreter returns a detailed type error rather than coercing values. This article examines the source code implementation, error handling mechanisms, and practical

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