Feature flags

Feature flags enable experimental or other opt-in features. They must be specified in the pipeline script.

warning

Feature flags with the nextflow.preview prefix can cause pipelines run with newer versions of Nextflow to fail due to breaking changes. Always consult the migration notes before updating to a new Nextflow version.

nextflow.enable.configProcessNamesValidation

Deprecated in version 25.10.0

Use the strict syntax instead. It validates process selectors without producing false warnings.

When true, prints a warning for every withName: process selector that doesn't match a process in the pipeline (defaulttrue).

nextflow.enable.dsl

Deprecated in version 25.04.0

Defines the DSL version to use (1 or 2).

nextflow.enable.moduleBinaries

When true, enables the use of modules with binary scripts. See Module binaries for more information.

nextflow.enable.strict

Deprecated in version 26.04.0

When true, executes the pipeline in "strict" mode, which introduces the following rules:

• When reading a params file, Nextflow will fail if a dynamic param value references an undefined variable

• When merging params from a config file with params from the command line, Nextflow will fail if a param is specified from both sources but with different types

• When using the join operator, the failOnDuplicate option is true regardless of any user setting

• When using the join operator, the failOnMismatch option is true (unless remainder is also true) regardless of any user setting

• When using the publishDir process directive, the failOnError option is true regardless of any user setting

• In a process definition, Nextflow will fail if an input or output tuple has only one element

• In a process definition, Nextflow will fail if an output emit name is not a valid identifier (i.e. it should match the pattern /[A-Za-z_][A-Za-z0-9_]*/)

• During a process execution, Nextflow will fail if a received input tuple does not have the same number of elements as was declared

• During a process execution, Nextflow will fail if the storeDir directive is used with non-file outputs

• Nextflow will fail if a pipeline param is referenced before it is defined

• Nextflow will fail if multiple functions and/or processes with the same name are defined in a module script

nextflow.preview.output

Added in version 24.04.0

Deprecated in version 25.10.0

This feature flag is no longer supported. Workflow outputs are out of preview.

When true, enables the use of workflow outputs.

nextflow.preview.recursion

Preview feature: the syntax and behavior may change in future releases.

When true, enables process and workflow recursion.

nextflow.preview.topic

Added in version 24.04.0

Deprecated in version 25.04.0

This feature flag is no longer supported. Topic channels are out of preview.

When true, enables the use of topic channels.

nextflow.preview.types

Added in version 25.10.0

Preview feature: the syntax and behavior may change in future releases.

When true, enables the use of typed processes. Must be enabled in every script that uses typed processes. Legacy processes cannot be defined in scripts with this flag enabled.