TDL

TDL, the Tesserae Data Language, is a small structure-only language for the files the Tesserae Shell reads: blocks, properties and values. tess_dl is the Python library that reads it into a tree that keeps everything in the file (comments, layout, positions), reports every mistake with file:line:column, and writes the text back unchanged except for an edit you ask for.

Status: alpha, package 0.1.1, language version 0.1. The import name changed from tdl to tess_dl in 0.1.1 (see CHANGELOG.md). The API may change before 1.0 (a minor version may break it; see docs/versioning.md). The language is in docs/language.md, the API in docs/api.md, the reasons for the choices in docs/decisions.md.

tess_dl needs Python 3.14 or later and has no dependencies:

pip install tesserae-dl

import tess_dl

text = """\
---
TDL: 0.1
Name: Shell_Root
---
Shell {
  Bar { Name: Top_Bar, Height: 32 }   # pixels
}
"""

doc = tess_dl.loads(text, path="Main_Shell.tdl")  # raises TDLSyntaxError on the first mistake
doc.root.type  # 'Shell'
doc.find("Shell_Root.Top_Bar").name  # 'Top_Bar'
assert tess_dl.dumps(doc) == text  # the exact text back, byte for byte

broken = text.replace("Height: 32", "Height 32")
result = tess_dl.parse(broken)  # never raises for a syntax error
[str(e) for e in result.errors]  # every error, in source order, up to 50

doc2 = doc.with_metadata("UID", "0192d3c4")  # one edit: every other byte is unchanged
doc3 = doc.find("Shell_Root.Top_Bar").with_property("Height", "40")

• loads, load (a binary file object), parse, dumps, dump.
• A tree of Document, Metadata, Block, Property, If, For and Comment, with Word, String, Number, Percent, Call, List, Slot and Template for values. Nodes are immutable, keep where they came from (node.origin), and are safe to share between threads.
• Edits return a new Document and change only the bytes they name: with_metadata, without_metadata, Block.with_property, replace. An edit that would break the file raises.
• 22 error codes, each with a plain message, a hint and a position (tdl-bare-hash: "This colour needs quotes. Quote the colour: "#ffffff""). The list is in docs/language.md.
• Limits (tess_dl.Limits): 1 MiB of text, 50 errors, 64 levels of nesting.
• Not in 0.1: checking keys or types (that is the program's, such as the shell), building a tree in code and formatting it, to_data(), a command line. See docs/api.md.

A 100 KB file reads in about 13 ms and a file at the 1 MiB limit in about 140 ms (docs/benchmarks.md).

PyPI name: tesserae-dl. Import name: tess_dl.

The conformance corpus

tests/corpus/ holds the files and expected results that define the language: valid files with their normalised content, files with each error and its position, and edits with their result. It ships in the source distribution (not in the wheel) as test data, and the Tesserae Shell reads it. New cases come from a TDL-REQ-### through the maintainer; see .agents/skills/conformance-corpus/SKILL.md.

Development

uv pip install -e . --group dev   # into the active venv (Python 3.14+)
python tools/check.py             # ruff, format check, mypy (strict), pytest: what CI runs
python benchmarks/bench.py        # timing against the budget (docs/benchmarks.md)

Work is tracked on the Tesserae Data Language board (python tools/board.py status). Agent instructions are in AGENTS.md; project skills are in .agents/skills/.

Versioning

See docs/versioning.md.

Licence

MIT