Reports

Nextflow provides several reporting mechanisms to analyze and debug pipeline runs:

• Execution log: Command to query information about past runs

• Execution report: Comprehensive HTML report for a pipeline run

• Execution timeline: HTML timeline of tasks executed in a pipeline run

• Trace file: CSV file with detailed task metrics for a pipeline run

• Workflow diagram: Graph visualization of pipeline structure

Execution log

The nextflow log command shows information about past pipeline runs and task executions. You can query by run name or session ID, and the command provides multiple options to filter and format the output.

By default, nextflow log prints the list of pipeline runs:

$ nextflow log
TIMESTAMP               DURATION        RUN NAME                STATUS  REVISION ID     SESSION ID                              COMMAND
2025-12-09 11:43:18     1s              naughty_heisenberg      OK      2ce0b0e294      bae65ec6-a2b9-49bf-b63e-2fec91945e48    nextflow run hello
2025-12-09 11:43:28     931ms           thirsty_swanson         OK      2ce0b0e294      bae65ec6-a2b9-49bf-b63e-2fec91945e48    nextflow run hello -resume
2025-12-09 11:43:37     8.5s            goofy_kilby             OK      ca20a6dfd2      d0a60572-076e-451a-b10e-16059ed77e36    nextflow run rnaseq-nf -profile conda

Providing a run name or session ID prints the tasks executed by that pipeline run:

$ nextflow log goofy_kilby
/Users/user/workspace/work/e1/fc2d06782f8263476426c576888033
/Users/user/workspace/work/72/f0542cfa81ad6abeaf1adf02e5cc2b
/Users/user/workspace/work/83/009346a3958358bb704e996d935c7a
/Users/user/workspace/work/84/15e4cd16df1db6f9bc0e22cc05316d

Customizing fields

The -f (-fields) option specifies which fields to include in the log.

nextflow log <run_name> -f [fields]

You can set a custom list of fields to focus on specific information. For example, hash, name, exit, and status:

$ nextflow log goofy_kilby -f hash,name,exit,status
e1/fc2d06       RNASEQ:INDEX  (ggal_1_48850000_49020000) 0       COMPLETED
72/f0542c       RNASEQ:FASTQC (ggal_gut)                 0       COMPLETED
83/009346       RNASEQ:QUANT  (ggal_gut)                 0       COMPLETED
84/15e4cd       MULTIQC                                  0       COMPLETED

Run the log command with the -l option to see the full list of fields. See log for more information.

Templates

The -t option specifies a template (string or file) to use when inspecting a single run:

nextflow log <run_name> -t <template> > <report>

You can create a template. For example, in Markdown:

## $name

script:

    $script

exit status: $exit
task status: $status
task folder: $folder

Then, use it to create a report:

nextflow log goofy_kilby -t my-template.md > execution-report.md

Filtering

The filter option selects which entries to include in the log.

nextflow log <run_name> -filter '<filters>'

Any valid Groovy boolean expression on the log fields can be used to define the filter condition. For example, you can filter for task names matching a pattern:

nextflow log goofy_kilby -filter 'name =~ /hello.*/ && status == "FAILED"'

Execution report

The execution report is an HTML report that includes metrics about a pipeline run. The report is organized into three sections: Summary, Resources, and Tasks.

To enable the execution report, add the -with-report option when launching a pipeline run:

nextflow run <pipeline> -with-report [file_name]

You can also enable the report in your Nextflow configuration:

report {
    enabled = true
    file = 'report.html'
}

See report for the list of available config options.

Summary

The Summary section reports the execution status, the launch command, overall execution time, and other workflow metadata:

Resource usage

The Resources section plots the distribution of resource usage for each workflow process using the interactive plotly.js plotting library.

Plots are shown for CPU, memory, job duration, and disk I/O. Each usage metric is shown both in raw form and as a percentage of the requested resources. These plots are helpful to check that task resources are used efficiently.

For information about how resource usage is computed, see Understanding task resource metrics.

Tasks

The Tasks section lists all executed tasks, reporting the status, command script, and other metrics for each task:

The same caveats for the trace file also apply to the task table.

Execution timeline

The execution timeline is an HTML report that shows a timeline of the tasks executed in a pipeline run:

The x-axis shows elapsed time relative to workflow launch. The y-axis shows a bar for each task execution. Each bar has the following properties (with the equivalent trace fields in parentheses):

• Bar length: Task duration (duration)

• Bar color: Identifies tasks from the same process

• Colored area: Real execution time (realtime)

• Gray area (left): Task scheduling time (start - submit)

• Gray area (right): Task termination time (complete - start - realtime)

• Label: Task duration (duration) and peak memory usage (peak_rss)

To enable the execution timeline, add the -with-timeline option when launching a pipeline run:

nextflow run <pipeline> -with-timeline [file_name]

You can also enable the execution timeline in your Nextflow configuration:

timeline {
    enabled = true
    file = 'timeline.html'
}

See timeline for the list of available config options.

Trace file

The trace file is a CSV file containing information about each task executed in a pipeline run, including submission time, start time, completion time, CPU usage, and memory usage.

To create the trace file, add the -with-trace option when launching a pipeline:

nextflow run <pipeline> -with-trace

The above command creates a file named trace.txt in the current directory. For example:

task_id	hash	native_id	name	status	exit	submit	duration	realtime	%cpu	peak_rss	peak_vmem	rchar	wchar
19	45/ab752a	2032	blast (1)	COMPLETED	0	2014-10-23 16:33:16.288	1m	5s	0.0%	29.8 MB	354 MB	33.3 MB	0
20	72/db873d	2033	blast (2)	COMPLETED	0	2014-10-23 16:34:17.211	30s	10s	35.7%	152.8 MB	428.1 MB	192.7 MB	1 MB
21	53/d13188	2034	blast (3)	COMPLETED	0	2014-10-23 16:34:17.518	29s	20s	4.5%	289.5 MB	381.6 MB	33.3 MB	0
28	b4/0f9613	2041	exonerate (1)	COMPLETED	0	2014-10-23 16:38:19.657	1m 30s	1m 11s	94.3%	611.6 MB	693.8 MB	961.2 GB	6.1 GB
31	d7/eabe51	2042	exonerate (3)	COMPLETED	0	2014-10-23 16:45:50.846	3m 1s	2m 6s	130.1%	703.3 MB	760.9 MB	1.1 TB	28.6 GB
30	4f/1ad1f0	2043	exonerate (2)	COMPLETED	0	2014-10-23 16:45:50.961	10m 2s	9m 16s	95.5%	706.2 MB	764 MB	1.6 TB	172.4 GB
52	72/41d0c6	2055	similarity (1)	COMPLETED	0	2014-10-23 17:13:23.543	30s	352ms	0.0%	35.6 MB	58.3 MB	199.3 MB	7.9 MB
53	3e/bca30f	2061	similarity (2)	COMPLETED	0	2014-10-23 17:13:23.770	30s	238ms	0.0%	6.7 MB	29.6 MB	190 MB	91.2 MB
54	8b/d45b47	2062	similarity (3)	COMPLETED	0	2014-10-23 17:13:23.808	30s	442ms	0.0%	108.1 MB	158 MB	832 MB	565.6 MB
98	de/d6c0a6	2099	matrix (1)	COMPLETED	0	2014-10-23 17:14:27.139	30s	1s	0.0%	4.8 MB	42 MB	240.6 MB	79 KB

The following caveats apply to trace metrics:

• Nextflow collects trace metrics through a background process for each job in the target environment. Make sure the following tools are available in the environment where tasks are executed: awk, date, grep, ps, sed, tail, tee. Container images that do not include all of these tools may lead to missing data.

• Trace metrics provide an estimation of the resources used by running tasks. They are not an alternative to low-level performance analysis tools, and they may not be accurate for very short-lived tasks (e.g., less than a few seconds).

• Some trace metrics are not reported when running on macOS.

You can also enable the trace file in your Nextflow configuration:

trace {
    enabled = true
    file = 'trace.txt'
}

See trace for the list of available config options.

Workflow diagram

A Nextflow pipeline can be represented as a directed acyclic graph (DAG). The vertices in the graph represent the pipeline’s processes and operators, while the edges represent the data dependencies (i.e., channels) between them.

To render the workflow DAG, run your pipeline with the -with-dag option. By default, it creates a file named dag-<timestamp>.html with the workflow DAG rendered as a Mermaid diagram.

The workflow DAG can be rendered in a different format by specifying an output file name with a different extension based on the desired format. For example:

nextflow run <pipeline> -with-dag flowchart.png

Tip

Use the -preview option with -with-dag to render the workflow DAG without executing any tasks.

The following example shows the Mermaid diagram for the rnaseq-nf pipeline (using the Mermaid Live Editor with the default theme):

nextflow run rnaseq-nf -preview -with-dag

%%{ init: { 'theme': 'base', 'themeVariables': { 'primaryColor': '#B6ECE2', 'primaryTextColor': '#160F26', 'primaryBorderColor': '#065647', 'lineColor': '#545555', 'clusterBkg': '#BABCBD22', 'clusterBorder': '#DDDEDE', 'fontFamily': 'arial' } } }%% flowchart TB subgraph " " v0["Channel.fromFilePairs"] v1["transcriptome"] v7["config"] end subgraph RNASEQ v2([INDEX]) v3([FASTQC]) v4([QUANT]) end v8([MULTIQC]) subgraph " " v9[" "] end v5(( )) v0 --> v3 v0 --> v4 v1 --> v2 v2 --> v4 v3 --> v5 v4 --> v5 v7 --> v8 v5 --> v8 v8 --> v9

See dag for the list of available config options.