Core Concepts

Pipeline

A pipeline is a YAML file that describes how data should be transformed. It has four top-level fields:

id: my-pipeline        # identifier used in console output

input:
  format: csv          # how to parse stdin

steps:                 # ordered list of transformations
  - normalize:
      fields:
        email: lower

output:
  format: jsonl        # how to write the result

The runtime flow is:

1. Parse stdin using input.format
2. Run each step in order, passing the payload from one to the next
3. Write the final payload to stdout using output.format

Step

A step is a single transformation applied to the payload. Each step in the steps list is a single-key object where the key is the step type and the value is its configuration:

steps:
  - normalize:          # step type
      fields:           # step configuration
        email: lower
  - redact:
      fields: [password]
      strategy: mask

Steps run in order. If any step fails, the pipeline stops and an error is printed.

See the Step Reference for all available steps.

Payload

The payload is the data flowing through the pipeline. It starts as the parsed contents of stdin and is passed from step to step. Three payload formats are supported:

Format	Description
json	A single JSON object or a JSON array of objects
jsonl	One JSON object per line (newline-delimited JSON)
csv	Comma-separated values with a header row

Every step declares which payload types it supports. If a step receives an unsupported payload type, the pipeline fails with a clear error.

Use the convert step to change the payload format mid-pipeline.

Input and output format

The input.format tells pipectl how to parse stdin. The output.format tells it how to serialise the final payload to stdout.

They do not need to match — you can read CSV and write JSONL, for example.

input:
  format: csv
output:
  format: jsonl

CSV delimiter

If your CSV uses a non-standard separator, set delimiter under input:

input:
  format: csv
  delimiter: ";"

Records

Steps that filter, sort, or count operate on records — the individual items within the payload:

Payload	Records
JSON array	Each element of the array
JSON object	A single record
JSONL	Each line
CSV	Each data row (excluding the header)

Nested fields

For JSON and JSONL payloads, some steps support dot notation and array indexing to reference nested fields:

- cast:
    fields:
      user.age:
        type: int
      tags[0]:
        type: string

CSV headers with dots (e.g. user.name) are automatically treated as nested objects when converting to JSON/JSONL.