Format in which each line holds a single JSON object. Fine-tuning training data and batch input files must use it, so CSV, TSV or one big JSON array may be rejected; ordinary REST calls don't involve it.
Also called JSON Lines.
Read more: Microsoft Learn
In the Ultra Transcenders books
AI-901AI-300AI-103DP-600DP-700
Each book explains JSONL in context, with comparison tables and the common traps.
Terms in this definition
- FORMAT
A DAX function that turns a value into text according to a format string, for instance "MMMM" to show a month's name. Since the output is text, numeric operations can't use it, and dynamic format strings were introduced to get around that.
- JSON
Text-based format for structured data. ARM templates and Cosmos DB documents are written in it, and most Azure REST APIs exchange request and response bodies as application/json.
- Fine-tuning
Continuing to train a pretrained base model on task examples, through supervised fine-tuning, DPO or RFT, so its weights shift towards a style, format or task. It neither acts as a safety control nor adds new knowledge well.
- Cluster Shared Volumes
Shared failover cluster storage that all nodes write to simultaneously, typically for Scale-Out File Server or Hyper-V. On SAN-backed storage, ReFS-formatted volumes work in redirected mode.
- TSV
Tab-separated values: a delimited text format similar to CSV but using a tab character between fields.
- REST
Short for representational state transfer, the style of HTTP API that Azure services expose.
Related terms
- OPENROWSET
Lets Fabric's T-SQL engines treat data files in Azure storage or OneLake (Parquet, CSV or JSONL) as a table. That is handy for peeking at a file, or for loading it with INSERT ... SELECT or CTAS.
- Vision fine-tuning
Fine-tuning where the JSONL messages include images as URLs or base64. Only gpt-4o (2024-08-06) and gpt-4.1 (2025-04-14) support it, and images showing people, faces or CAPTCHAs are dropped.