# JSON Unflattener Convert flattened key-value pairs back to nested JSON objects with support for different key formats and data type inference > Canonical page: https://elysiatools.com/en/tools/json-unflattener - **Category:** Data Processing - **Keywords:** json, unflatten, nested, object, reconstruct, key-value, restore ## Overview The JSON Unflattener tool allows you to instantly convert flattened key-value pairs or dot-notation strings back into structured, nested JSON objects. It is designed to help developers and data analysts reconstruct complex data hierarchies from flat exports, CSVs, or configuration files with ease. ## Inputs - **Flattened Data Input** (textarea): Enter your flattened key-value pairs... - **Input Format** (select) - **Key Format** (select) - **Key Delimiter** (text): Character separating nested keys - **Data Type Inference** (select) - **Array Detection** (select) - **Merge Strategy for Conflicts** (select) - **Preserve Empty/Null Values** (checkbox) ## When to use - Reconstructing nested JSON objects from flat database exports or CSV files. - Converting dot-notation configuration strings into readable hierarchical JSON structures. - Standardizing inconsistent data formats by parsing flattened keys into a clean, nested schema. ## How it works - Paste your flattened data into the input area and select your input format (JSON or Key=Value). - Choose the appropriate key format (e.g., Dot Notation, Bracket, or Path) to match your input structure. - Configure data type inference and array detection settings to ensure the output matches your expected schema. - Click process to generate and download your fully nested, structured JSON object. ## Use cases - Transforming flat environment variable exports into nested application configuration files. - Rebuilding complex API response objects from flattened log data for debugging purposes. - Cleaning up exported spreadsheet data that uses dot-notation headers to represent nested object properties. ## Frequently asked questions ### What input formats are supported? You can provide input as a flat JSON object or as a list of Key=Value pairs, one per line. ### How does the tool handle arrays? The tool supports numeric keys (e.g., user.0, user.1) or bracket notation (e.g., user[0], user[1]) to automatically detect and reconstruct arrays. ### Can it automatically detect data types? Yes, the 'Auto-detect' and 'Smart' inference modes automatically convert strings into numbers, booleans, or null values where applicable. ### What happens if there are conflicting keys? You can choose a merge strategy: override the existing value, merge objects/arrays, or trigger an error if a conflict is detected. ### Is my data processed on a server? The tool performs processing locally in your browser, ensuring your data remains private and secure. ## Related tools - [JSON Data Lineage Tracer](https://elysiatools.com/en/tools/json-data-lineage-tracer): Trace JSON field paths, derived dependencies, and transformation history to build a field-level lineage graph - [JSON Key Renamer](https://elysiatools.com/en/tools/json-key-renamer): Batch rename JSON object keys with support for patterns, rules, and transformations. Perfect for API response formatting and data normalization. - [BOM Character Remover](https://elysiatools.com/en/tools/data-bom-remover): Remove BOM (Byte Order Mark) characters from text and file content. Perfect for cleaning up text files that have encoding issues, fixing CSV imports, and preparing data for processing. Features: - Detect and remove UTF-8 BOM (EF BB BF) - Detect and remove UTF-16 BOM (FE FF or FF FE) - Detect and remove UTF-32 BOM (00 00 FE FF or FF FE 00 00) - Support multiple input formats - Visual BOM character display - Detailed detection report - Support for batch text processing Common Use Cases: - Fix CSV file import errors - Clean up text file encoding issues - Prepare data for JSON parsing - Fix XML parsing problems - Resolve API data encoding conflicts - Standardize text data format - [JSON Key Extractor](https://elysiatools.com/en/tools/json-key-extractor): Extract all keys from JSON objects with multiple output formats. Perfect for analyzing JSON structure, documentation generation, and understanding complex nested objects. - [Object Key-Value Converter](https://elysiatools.com/en/tools/object-key-value-converter): Convert between different object key-value formats and manipulate object structures - [CSV to JSON Converter](https://elysiatools.com/en/tools/csv-to-json): Convert CSV data to JSON format with customizable parsing options - [Excel to JSON Converter](https://elysiatools.com/en/tools/excel-to-json): Convert Excel file to JSON format, extracting data from the first worksheet - [Lodash Online Utility](https://elysiatools.com/en/tools/lodash-online-utility): Run a safe, curated set of Lodash helpers on JSON input. ## Samples - [JSON Samples](https://elysiatools.com/en/samples/json): JSON (JavaScript Object Notation) format examples from simple to complex structures - [Terraform Plan JSON Samples](https://elysiatools.com/en/samples/terraform-plan-json-samples): Sample Terraform plan JSON files exported from terraform show -json style payloads for dependency visualization and change review - [Chat Transcript JSON Samples](https://elysiatools.com/en/samples/chat-transcript-json): JSON examples for multi-role chat transcripts - [Rich Media JSON Samples](https://elysiatools.com/en/samples/rich-media-json): JSON examples for popular rich text editors (TipTap, Quill, Slate)