protocol. The main benefit of using it is to avoid the cost of starting up a new _Black_
process every time you want to blacken a file.
+```{warning}
+`blackd` should not be run as a publicly accessible server as there are no security
+precautions in place to prevent abuse. **It is intended for local use only**.
+```
+
## Usage
`blackd` is not packaged alongside _Black_ by default because it has additional
The headers controlling how source code is formatted are:
- `X-Line-Length`: corresponds to the `--line-length` command line flag.
+- `X-Skip-Source-First-Line`: corresponds to the `--skip-source-first-line` command line
+ flag. If present and its value is not an empty string, the first line of the source
+ code will be ignored.
- `X-Skip-String-Normalization`: corresponds to the `--skip-string-normalization`
command line flag. If present and its value is not the empty string, no string
normalization will be performed.
- `X-Skip-Magic-Trailing-Comma`: corresponds to the `--skip-magic-trailing-comma`
- command line flag. If present and its value is not the empty string, trailing commas
+ command line flag. If present and its value is not an empty string, trailing commas
will not be used as a reason to split lines.
+- `X-Preview`: corresponds to the `--preview` command line flag. If present and its
+ value is not an empty string, experimental and potentially disruptive style changes
+ will be used.
- `X-Fast-Or-Safe`: if set to `fast`, `blackd` will act as _Black_ does when passed the
`--fast` command line flag.
- `X-Python-Variant`: if set to `pyi`, `blackd` will act as _Black_ does when passed the