YAML has its idiosyncrasies, like all input formats. We attempt to list some common problems here.

Validate your files offline before uploading.

Try pasting your text into an online YAML validator (find several with Google) like YAML Lint . Or write some code that parses YAML using one of the available libraries for different languages.

Even better: install the Python hepdata-validator package which checks that the YAML files match the HEPData schema. Then write a script to validate your YAML files offline. Here is a simple example which validates the submission.yaml file and all data files against the HEPData schema if the hepdata-validator package is installed, otherwise it performs a more basic (but still useful) check that the files are valid YAML.

An alternative validation script has been written in Python 3 by Christian Holm Christensen (see #8), which reimplements (and attempts to improve) the main functionality of the hepdata-validator package.

Escape special characters.
Some characters in YAML need to be escaped, otherwise they cause errors when parsing. The two characters that cause most trouble for YAML are : and -. Other problematic characters are {, }, and %. So if you use these characters in some description string, please make sure you put quotes around the whole string.
Ensure spaces after colons.
Another annoyance can be with spacing. {symerror:0.4, label:stat} will give you an error. Change this to {symerror: 0.4, label: stat} however and everything will work nicely.
Use --- to separate tables in the submission.yaml file.
A line --- separates YAML documents in the same file and is used to denote the start of a new table in the submission.yaml file. But don’t end the submission.yaml file with --- otherwise a final (empty) table will be created, which might cause some problems.
Optionally include thumbnail images.

Thumbnail images of the original figures can be displayed alongside the tables as in the example above:

- {description: Image file, location: figFigure8A.png}
- {description: Thumbnail image file, location: thumb_figFigure8A.png}

The image files should be included in the submitted archive. Note that thumbnail images need to have a filename beginning with thumb_.

The table name should not be too lengthy.
There are no formal restrictions imposed on the name of a table, other than requiring it to be 64 characters or less. The standard convention is to use “Table 1”, “Table 2”, etc. However, it might be useful to give more descriptive name values. Complex table names, in particular, containing special characters, were initially not completely supported by the HEPData code. These initial problems should now have been resolved.
Use only simple HTML in comments and descriptions
Limited HTML markup is allowed in the comment and description fields, as shown in the following table. Disallowed HTML tags will be escaped, and disallowed HTML attributes will be removed. In some cases your HTML may not appear as expected; in this case please remove any disallowed tags and attributes and try again. If you are using < or > signs and they do not appear as expected, try escaping them, i.e. replace < with &lt; and > with &gt;.
Allowed HTML tags and attributes
Tag Allowed attributes
a href, title, name, rel
abbr title
acronym title