Besides XML is not universally loved.
It looks great, then you design your stuff and it goes great, then you deploy to the real world and everything catches on fire instantly and everytime you stop one another one starts.
Generally speaking I feel like this is true for a lot of stuff in programming circles, XML included.
New technology appears, some people play around with it. Others come up with using it for something else. Give it some time, and eventually people start putting it everywhere. Soon "X is not for Y" blogposts appear, and usage finally starts to decrease as people rediscover "use the right tool for the right problem". Wait yet some more time, and a new technology appears, and the same cycle begins again.
Seen it with so many things by now that I think "we'll" (the software community) forever be stuck in this cycle and the only way to win is to explicitly jump out of the cycle and watch it from afar, pick up the pieces that actually make sense to continue using and ignore the rest.
We eventually said, "what if we made databases based on JSON" and then came MongoDB. Worse performance than a relational database, but who cares! It's JSON! People have mostly moved away from document databases, but that's because they realized it was a bad idea for the majority of usecases.
I think the only left out part is about people currently believing in the current hyped way, "because this time it's right!" or whatever they claim. Kind of the way TypeScript people always appear when you say that TypeScript is currently one of those hyped things and will eventually be overshadowed by something else, just like the other languages before it, then soon sure enough, someone will share why TypeScript happen to be different.
>wasting cycles to manifest structured data in an unstructured textual format
JSON IS a structured textual format you dofus. What you're complaining about is that the message defines its own schema.
>has massive overhead on the source and destination sides
The people that care about the overhead use MessagePack or CBOR instead.
I personally hope that I will never have to touch anything based on protobufs in my entire life. Protobuf is a garbage format that fails at the basics. You need the schema one way or another, so why isn't there a way to negotiate the schema at runtime in protobuf? Easily half or more of the questionable design decisions in protobuffers would go away if the client retrieved the schema at runtime. The compiler based workflow in Protobuf doesn't buy you a significant amount of performance in the average JS or JVM based webserver since you're copying from a JS object or POJO to a native protobuf message anyway. It's inviting an absurd amount of pain for essentially zero to no benefits. What I'm seeing here is a motte-bailey justification for making the world a worse place. The motte being the argument that text based formats are computationally wasteful, which is easily defended. The bailey being the implicit argument that hard coding the schema the way protobuf does is the only way to implement a binary format.
Note that I'm not arguing particularly in favor of MessagePack here or even against protobuf as it exists on the wire. If anything, I'm arguing the opposite. You could have the benefits of JSON and protobuf in one. A solution so good that it makes everything else obsolete.
Please avoid snark.
https://en.wikipedia.org/wiki/XML_appliance
E.g.
https://www.serverwatch.com/hardware/power-up-xml-data-proce...
i don't believe this is true. machine language doesn't need the kind of verbosity that xml provides. sgml/html/xml were designed to allow humans to produce machine readable data. so they were meant for humans to talk to machines and vice versa.
I think part of the problem is focusing on the wrong aspect. In the case of XSLT, I'd argue its most important properties are being pure, declarative, and extensible. Those can have knock-on effects, like enabling parallel processing, untrusted input, static analysis, etc. The fact it's written in XML is less important.
Its biggest competitor is JS, which might have nicer syntax but it loses those core features of being pure and declarative (we can implement pure/declarative things inside JS if we like, but requiring a JS interpreter at all is bad news for parallelism, security, static analysis, etc.).
When fashions change (e.g. XML giving way to JS, and JSON), we can end up throwing out good ideas (like a standard way to declare pure data transformations).
(Of course, there's another layer to this, since XML itself was a more fashionable alternative to S-expressions; and XSLT is sort of like Lisp macros. Everything old is new again...)
Features are now available like key (index) to greatly speedup the processing. Good XSLT implementation like Saxon definitively helps as well on the perf aspect.
When it comes to transform XML to something else, XSLT is quite handy by structuring the logic.
XSLT 2+ was more about side effects.
I never really grokked later XSLT and XPath standards though.
XSLT 1.0 had a steep learning curve, but it was elegant in a way poetry is elegant because of extra restrictions imposed on it compared to prose. You really had to stretch your mind to do useful stuff with it. Anyone remembers Muenchian grouping? It was gorgeous.
Newer standards lost elegance and kept the ugly syntax.
No wonder they lost mindshare.
My biggest problem with XSLT is that I've never encountered a problem that I wouldn't rather solve with an XPath library and literally any other general purpose programming language.
When XSLT was the only thing with XPath you could rely on, maybe it had an edge, but once everyone has an XPath library what's left is a very quirky and restrictive language that I really don't like. And I speak Haskell, so the critic reaching for the reply button can take a pass on the "Oh you must not like functional programming" routine... no, Haskell is included in that set of "literally any other general purpose programming language" above.
There's clearly value in XSLT's near-universal support as a web-native system. It provides templating out of the box without invoking JavaScript, and there's demand for that[1]. But it still lacks decent in-browser debugging which JS has in spades.
[1] https://justinfagnani.com/2025/06/26/the-time-is-right-for-a...
XML (the data structure) needs a non-XML serialization.
Similar to how Semantic Web's Owl has four different serializations, only one of them being the XML serialization. (eg. Owl can be represented in Functional, Turtle, Manchester, Json, and N-triples syntaxes.)
That's YAML, and it is arguibly worse. Here's a sample YAML 1.2 document straight from their spec:
%TAG !e! tag:example.com,2000:app/
---
- !local foo
- !!str bar
- !e!tag%21 baz
--
Some notes:
- SemWeb also has JSON-LD serialization. It's a good compromise that fits modern tooling nicely.
- XML is still a damn good compromise between human readable and machine readable. Not perfect, but what is perfect anyway?
- HTML5 is now more complex than XHTML ever was (all sorts of historical caveats in this claim, I know, don't worry).
- Markup beauty is relative, we should accept that.
- Xee: https://github.com/Paligo/xee
- xrust: https://docs.rs/xrust/latest/xrust/xslt/
- XJSLT (compiles XSLT to JS): https://github.com/egh/xjslt
Xee is WIP AFAIK and I don't know the maturity of xrust and XJSLT.
Streaming is not supported until later version.
How, where? In 2013 I was still working a lot with XSLT and 1.0 was completely dead everywhere one looked. Saxon was free for XSLT 2 and was excellent.
I used to do transformation of both huge documents, and large number of small documents, with zero performance problems.
Obviously, that means there's a lot of legacy processes likely still using it.
The easiest way to improve the situation seems to be to upgrade to a newer version of XSLT.
In the early days the xsl was all interpreted. And was slow. From ~2004 or so, all the xslt engines came to be jit compiled. XSL benchmarks used to be a thing, but rapidly declined in value from then onward because the perf differences just stopped mattering.
I'm pretty sure that's because implementing XSLT 2.0 needs a proprietary library (Saxon XSLT[0]). It was certainly the case in the oughts, when I was working with XSLT (I still wake up screaming).
XSLT 1.0 was pretty much worthless. I found that I needed XSLT 2.0, to get what I wanted. I think they are up to XSLT 3.0.
I think the guy behind Saxon may be one of the XSLT authors.
But in the end the core problem is XSLT, the language. Despite being a complete programming language, your options are very limited for resolving performance issues when working within the language.
I worked with a guy who knew all about complexity analysis, but was quick to assert that "n is always small". That didn't hold - but he'd left the team by the time this became apparent.
A couple of blue chip websites I‘ve seen that could be completely taken down just by requesting the sitemap (more than once per minute).
PS: That being said it is an implantation issue. But it may speak for itself that 100% of the XSLT projects I‘ve seen had it.