Spectral - Flexible JSON linter with out of the box support for OpenAPI v2 and v3.
Ajv - Fastest JSON Schema Validator.
jtc - JSON processing utility.
JSMN - World fastest JSON parser/tokenizer.
Verify JSON - Library to verify JSON structure easily using a lightweight JSON schema syntax. (HN)
jq - Command-line JSON processor.
jq-repl - REPL to make exploring data with JQ easier.
pdiffjson - Diff JSON the easy way.
flatted - Fast and minimal circular JSON parser.
ImportJSON - Import JSON into Google Sheets, this library adds various ImportJSON functions to your spreadsheet.
Cambria - JavaScript/Typescript library for converting JSON data between related schemas.
YYJSON - High performance JSON library written in ANSI C.
RapidJSON - Fast JSON parser/generator for C++ with both SAX/DOM style API.
query-json - Faster and simpler implementation of jq in Reason Native. (Article)
json-schema-to-typescript - Compile JSONSchema to TypeScript type declarations.
wernicke - Redaction tool for structured data.
Hjson - User interface for JSON.
JMESPath - Query language for JSON. (go-jmespath)
Nesting levels for JSON parsers - Documenting how JSON parsers of several programming languages deal with deeply nested structures.
TypeBox - JSON Schema Type Builder with Static Type Resolution for TypeScript.
JSON Schema $Ref Parser - Parse, Resolve, and Dereference JSON Schema $ref pointers.
jose - Universal "JSON Web Almost Everything" - JWA, JWS, JWE, JWT, JWK with no dependencies.
JSON Schema Viewer - JavaScript tool for visualizing json-schemas. (Code)
JQL - JSON Query Language CLI tool.
Jansson - C library for encoding, decoding and manipulating JSON data.
json-rules-engine - Rules engine expressed in JSON.
JSON Editor - JSON Schema Based Editor. (Code)
JSON-LD Schema - Simple schema validation for linked data.
cJSON - Ultralightweight JSON parser in ANSI C.
JSONLint - JSON Validator.
HuJSON - JSON for Humans (comments and trailing commas).
JsonLogic - Build complex rules and share them as JSON.