JSON Metrics output

[apeltzer]

I'd love to write a MultiQC module for this, but in order to facilitate this, would it be possible to write outputs in a JSON format for easier parsing?

e.g. FASTP does this, so we can directly load the metrics to show them in a MultiQC report. I'm working on a small validator workflow that includes fq_lint and it works nicely, but making the metrics directly accessible in a larger table would be really cool.

https://github.com/MultiQC/MultiQC/blob/main/multiqc/modules/fastp/fastp.py as an example how the JSON could look like.

https://github.com/MultiQC/test-data/tree/main/data/modules/fastp

Not too familiar with rust, otherwise I'd have opened a PR already ;-)

[keirsalterego]

Hi @apeltzer and team,

I’m Manish, a 3rd-year Computer Science undergrad. I've been exploring the St. Jude Rust Labs ecosystem and am interested in picking this issue up.

I am planning to apply for GSoC 2026, so I am starting my contributions early to get familiar with the codebase. I reviewed the fastp integration you linked, and I see why a structured JSON output is critical for the MultiQC module.

My plan to implement this:

1. Pipeline Safety: Instead of printing to stdout (which might interfere with piping FASTQ data), I propose adding a --json-output <PATH> argument. This ensures we can generate the report without breaking downstream tools.
2. Schema Design: I will define a serializable struct that mirrors the hierarchy of the fastp JSON (grouping metrics by summary, read_counts, etc.) to make the MultiQC integration seamless.
3. Implementation: Use serde_json to serialize the internal validation metrics into this new schema and write to the specified file path.

Does this approach align with your requirements? If so, I’m ready to start working on the PR.