XML vs TONL: Data Format Comparison for AI Applications

XML (eXtensible Markup Language) was the backbone of the enterprise web for two decades. It gave us SOAP, RSS, SVG, and configuration files for everything from Java Spring to Microsoft Office (`.docx` is just zipped XML).

Its premise was bold: a universal format that is both human-readable and machine-readable, capable of representing any hierarchy with strict validation.

But in the age of Generative AI, XML's greatest strength—its rigorous verbosity—has become its greatest weakness. TONL is the spiritual successor to XML for the AI era. It keeps the "Enterprise Grade" features (Schema, Querying, Namespaces) but discards the syntactic bloat that kills context window performance.

The Legacy of XML: Why it Ruled

Before we compare, we must respect the giant. XML introduced three game-changing concepts to data exchange:

1. Validation (XSD/DTD): You could mathematically prove a file was valid before processing it.
2. Querying (XPath): You could find data deep in a tree without parsing the whole structure in code.
3. Transformation (XSLT): You could reshape data declaratively.

JSON won the web by abandoning these features for simplicity. But now, as we build complex RAG pipelines and Agentic workflows, we find ourselves missing them. We need validation. We need querying.

TONL: Bringing Enterprise Power Back

TONL is what happens if you design XML today, knowing that "Token Count" is the scarcest resource in computing.

1. The Closing Tag Penalty

XML is redundant by design.

<customer>
  <id>12345</id>
  <name>Big Corp Inc.</name>
  <status>Active</status>
</customer>

Look at the repetition: `customer`, `id`, `name`, `status`. They appear twice.
Token Cost: ~25 tokens.

TONL uses indentation (like Python) to define scope.

customer:
  id: 12345
  name: Big Corp Inc.
  status: Active

Token Cost: ~12 tokens.
Savings: 52%.

For a 10MB XML dump, converting to TONL saves 5MB of text and cuts your API bill in half.

Query Capabilites: XPath vs TONL Query

XML gave us XPath, a powerful language for selecting nodes. TONL gives us a native Query API.

TONL's query syntax is closer to JavaScript/JSONPath, making it intuitive for modern developers, whereas XPath has a steep learning curve.

Schema Validation: XSD vs TSL

XSD (XML Schema Definition) is notoriously complex. It is XML describing XML.

<xs:element name="age">
  <xs:simpleType>
    <xs:restriction base="xs:integer">
      <xs:minInclusive value="0"/>
      <xs:maxInclusive value="120"/>
    </xs:restriction>
  </xs:simpleType>
</xs:element>

It takes 8 lines to say "Age is an integer between 0 and 120."

TSL (TONL Schema Language) is human-readable.

age: u8 min:0 max:120

One line. This simplicity encourages developers to actually write schemas, rather than skipping them because XSD is too hard.

Security: The XXE Nightmare

XML has a dangerous feature: External Entity Expansion (XXE).

<!DOCTYPE foo [ <!ENTITY xxe SYSTEM "file:///etc/passwd"> ]>
<foo>&xxe;</foo>

If a naive XML parser reads this, it will substitute `&xxe;` with the contents of your server's password file. This has been a top OWASP vulnerability for years.

TONL is Secure by Design. It does not support external entity loading or DTDs. You can parse untrusted TONL safely.

Attributes vs Elements vs Props

XML developers always argued: "Should ID be an attribute `<user id="1">` or an element `<user><id>1</id></user>`?"

TONL resolves this ambiguity. Everything is a Field.

user:
  id: 1
  name: Alice

There is no distinction between "metadata" and "data". This simplifies the mental model for both humans and AI.

Token Economics: The 69% Reduction

The savings when moving from XML to TONL are massive because:

• No Closing Tags: Saves 50% of structure tokens.
• No Brackets: `<` and `>` are gone.
• No Quotes for Numbers: XML often quotes attributes `count="10"`. TONL uses `count: 10`.

Use Cases

When to stick with XML

Legacy Integration.If you are connecting to a bank mainframe, a healthcare system (HL7 v3), or an old SOAP API, you have no choice. The world runs on legacy XML.

When to switch to TONL

Modern Enterprise Data Platform.If you want the strictness of XML (Schemas, Types, Validation) but you are building for the API Economy and AI, TONL is the upgrade.

It gives you the "Peace of Mind" of XML without the "Pain of Parsing."

Conclusion

XML was the right technology for the 2000s, where CPU cycles were cheap and bandwidth was the bottleneck (ironically, XML compression is good).

In the 2020s, Context Window is the bottleneck. Every token you feed an LLM costs money and reduces what else it can remember. TONL respects this constraint.

Retire your angle brackets. Adopt indentation.