Miller review
A free, open-source CLI for streaming transformations across structured data formats.
Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
Miller is an open-source command-line tool for processing name-indexed and tabular data. It is designed for users working with data cleaning, log processing, statistical reporting, database-query post-processing, and streaming workflows. The tool runs on Windows, macOS, and Linux, and handles formats including CSV, TSV, ASV, USV, JSON, JSON Lines, YAML, PPRINT, Markdown, XTAB, DKVP, DKVPX, NIDX, DCF, and recutils. Its interface is code-based, with pipe-friendly operation suited to Unix-style workflows.
Miller’s main strength is breadth within structured-data transformation. It can convert between supported formats, filter records, select fields, sort, join, group, reshape, aggregate, and report statistics. The Miller domain-specific language extends those operations with custom transformations. Input checks cover parseability and empty keys, while MCP tools support capability discovery, DSL validation, data description, and command execution. This combination makes Miller a practical fit when transformations need to be repeatable, composable, and expressed as commands or scripts rather than managed through a visual interface.
The published positioning centers on a free, open-source tool distributed as a command-line binary rather than a hosted service, so there are no paid tiers shaping its feature set. The self-hosted model suits technical teams that want local control and streaming execution, but it places installation, workflow design, and operational responsibility with the user. Miller is a strong choice for format conversion and structured-data processing in shell-based pipelines. Teams seeking hosted orchestration or a non-code transformation interface should choose a different type of product.
Miller pros and cons
- Where it wins
- Supports CSV, JSON, YAML, DCF, and many other formats
- Streams filtering, reshaping, joining, aggregation, and conversion
- Includes a dedicated language for custom transformations
- Where it doesn't
- Requires code-based command-line operation
- Self-hosted deployment puts setup responsibility on the operator
- Not positioned for external integrations or orchestration
Miller fact sheet, pricing and score →
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