YAMLRocks vs yamlium

yamlium is a pure-Python, dependency-free YAML library that preserves comments and structure through a manipulation API, a real feature for a zero-dependency package. Where YAMLRocks pulls ahead is everything around that: it is one to two orders of magnitude faster, it commits to YAML 1.2 and proves it against the test suite, and it adds native includes and schema validation that yamlium has no equivalent for.

Feature comparison

Feature	yamlium	YAMLRocks
Comment-preserving round-trip	Yes	Yes (byte-for-byte)
Native `!include` + writeback	No	Yes
JSON Schema validation	No	Yes (line-numbered)
Source line/column	No	Yes (annotated mode)
Verified vs the YAML suite	Not stated	Yes, in full
Declared YAML version	Undocumented	1.2 (1.1 optional)
Anchors / merge keys	Preserved / yes	Preserved / yes
Implementation	Pure Python	Rust extension
Speed (parse / dump)	baseline	~42x / ~11x faster

Speed: Rust vs pure Python

yamlium is pure Python, which makes it portable but slow. YAMLRocks does the same work in Rust, one to two orders of magnitude faster on both directions.

YAMLRocks vs yamlium on reading and writing: YAMLRocks is an order of magnitude faster on both loads and dumps.

Operation	yamlium	YAMLRocks	YAMLRocks is
Reading	~71 ms	~1.7 ms	~42x faster
Writing	~11 ms	~1.0 ms	~11x faster

Same round-trip, more of everything else

yamlium’s comment-and-structure-preserving editing is its selling point, and YAMLRocks matches it: load with OPT_ROUND_TRIP, edit through a node API, and re-emit with comments, anchors, and layout intact, byte-for-byte when unmodified. On that same foundation YAMLRocks adds what yamlium does not have:

Native !include with file-aware write-back across a split configuration.
JSON Schema validation with line-numbered errors.
Annotated mode with the source line and column on every node.
Safe-by-default loading and correct YAML 1.2 typing.

See round-trip editing, includes, schema validation, and annotated mode.

Correctness, verified rather than assumed

YAMLRocks commits to the YAML 1.2 core schema and checks it against the entire official test suite in CI. yamlium does not document which YAML version it targets, and its scalar resolution lands between the two in surprising ways:

import yamlrocks

yamlrocks.loads(b"mode: 0777")   # {'mode': '0777'}  a string, per YAML 1.2
yamlrocks.loads(b"mask: 0o17")   # {'mask': 15}      the 1.2 octal
# yamlium returns {'mode': 777} and {'mask': '0o17'}.

When you cannot tell which spec a library follows, you cannot tell what a value will become. YAMLRocks makes that explicit and pins it.

Where yamlium is a reasonable pick

yamlium is a fair choice when you specifically need a pure-Python, zero-dependency package (no binary wheel to install) and can accept its speed and its scalar quirks. Its comment-editing API is nicely done.

When to choose YAMLRocks

Choose YAMLRocks when you can install a wheel and want the same comment-preserving round-trip with real speed, native includes, schema validation, source locations, and correctness that is verified rather than undocumented.