# Fix Galaxy upload and datatype-detection problems

Fix wrong Galaxy dataset datatypes with a decision procedure: classify from observable evidence (binary-garbage preview or 0x8b UnicodeDecodeError means gzipped data labeled uncompressed; tool input dropdown missing the dataset means a datatype mismatch), then reassign via Edit Attributes Datatypes tab, keeping Upload on Auto-detect.

Exact reference: {"kind":"skill_version","skill_id":"skl_9DpMIz_MClXJJ7lrGGYGtw","version_id":"skv_7noHVlSXkW0W3Ss6W2asDA"}

Applicability: [{"constraint":"Galaxy releases with the Upload Auto-detect option and the Edit Attributes Datatypes tab","technology":"Galaxy","version_scheme":"unknown"}]

# Fix Galaxy upload and datatype-detection problems

Use this when uploaded data gets the wrong format, a tool's input dropdown
refuses to list your dataset, the preview shows garbage, or metadata setting
fails after upload. Galaxy tools only see datasets whose datatype they
accept, so a wrong datatype looks exactly like missing data — classify the
mismatch FIRST, then reassign.

## 1. How Galaxy assigns datatypes

- The Upload dialog has a **Type** option, default **Auto-detect**, which
  sniffs the format. Leave it on Auto-detect unless you have a specific
  reason not to — forced types are the most common source of these problems.
- After upload, the dataset's assigned datatype is shown in its expanded
  history view. A tool's input selector lists only datasets of compatible
  types.
- You can fix a wrong assignment at any time without re-uploading: click the
  pencil (Edit Attributes) icon → **Datatypes** tab → pick the correct type
  → Save. Re-detecting is cheaper than re-uploading, so try it first.

## 2. Classify from observable evidence

### A. Preview shows binary garbage or metadata fails with a decode error

Signature in the dataset's error/metadata log:

```
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x8b in position 1: invalid start byte
```

`0x8b` in position 1 is the tell: the bytes `1f 8b` are the gzip magic
number, so the file is gzip-compressed but was labeled as an uncompressed
type (`txt`, `fastqsanger`, ...). Fix: assign the matching `.gz` datatype
(e.g. `fastqsanger.gz`) via Edit Attributes → Datatypes, or re-upload with
Auto-detect. This also happens when a `.gz` file is renamed to drop the
extension before upload.

### B. A tool's input dropdown won't list the dataset

The dataset's datatype does not match the tool's accepted formats. Verify
the data genuinely *is* the format you want to claim (preview the first
lines), then reassign via the Datatypes tab. Two rules:

- Never assign a datatype the bytes don't conform to — the tool will fail
  or, worse, silently misbehave on mislabeled data.
- `fastq` vs `fastqsanger` is about quality-score encoding, not filename;
  pick by the actual encoding. The FASTQ Groomer tool can convert between
  FASTQ variants if you need a real conversion rather than a relabel.

### C. Auto-detect picks the wrong type

Don't fight the sniffer by forcing types blindly — inspect the file first:
preview the head of the dataset, check for compression (class A), check for
truncation or mixed content. For fastq and bam data, Auto-detect "should
always work well"; when it doesn't, suspect the file itself (corrupt,
truncated, or an unusual flavor) rather than the detector, and validate or
re-obtain the source file.

### D. The upload itself fails

The file never arrived — a network, quota, or source problem, not a
datatype problem. Do not reassign datatypes on a dataset that has no data.

## 3. Checklist

1. Leave Upload on Auto-detect; only set a type manually when you know the
   sniffer gets that source wrong.
2. Wrong type after upload → pencil icon → Datatypes tab → correct type →
   Save. Re-upload only if the bytes themselves are bad.
3. `0x8b` decode errors → compressed data with an uncompressed datatype;
   assign the `.gz` variant.
4. Tool can't see the dataset → datatype mismatch; confirm the bytes match
   before relabeling.
5. Still stuck → ask on help.galaxyproject.org with a shared history link;
   include the dataset's assigned datatype and the tool's expected format.


## Supporting basis and limitations

Built from Galaxy help-forum threads: the UnicodeDecodeError 'utf-8 codec can't decode byte 0x8b in position 1' metadata failure (gzipped data with an uncompressed datatype), and staff guidance to allow Galaxy to guess the datatype at upload and to use the pencil icon to re-detect the datatype, noting fastq and bam data work well with the guess.

## Change and rationale

New skill: diagnose and fix Galaxy upload datatype misassignment and detection problems.

Datatype misassignment is a recurring Galaxy help-forum topic where the standard staff advice is to let Auto-detect guess and to re-detect via the pencil icon rather than forcing types. Users instead relabel bytes to types they don't conform to, or re-upload repeatedly. A classify-first procedure keyed on concrete signatures (the 0x8b gzip tell, tool-input filtering) fixes the common cases without support intervention.