XML Envelope Format

The most common envelope format (~35%, ~18 tools) in the corpus. Instructions are wrapped in XML-style tags, providing hierarchical structure that LLMs parse well due to training on HTML/XML markup.

Structure (confidence: high)

<system>
  <role>You are an expert...</role>
  <tools>
    <tool name="search">...</tool>
  </tools>
  <rules>
    <rule>Never summarize...</rule>
  </rules>
</system>

Tag names serve as semantic anchors that improve instruction following.

Variants (confidence: high)

• Narrow XML (Anthropic, Cline): 3-5 top-level tags. Structured <tool> blocks.
• Wide XML (Manus Modules): 15+ <module> blocks, extremely verbose.
• Hybrid XML-Markdown (Cluely, CodeBuddy): XML envelope with markdown inside tags.
• Minimal XML (Perplexity, Notion AI): 2-3 XML tags, rest in markdown.

Format Selection Trade-offs (confidence: high)

Format	Token Efficiency	LLM Compliance	Human Editability	Machine Parseability
XML Envelope	Medium	High	Medium	High
Markdown Headers	High	High	High	Low
YAML Config	High	Low	Medium	High
JSON-Embedded	Medium	Medium	Low	High

Implications: XML dominates because it optimizes for the LLM’s parsing ability — the hierarchical structure and semantic tag names improve instruction following. The choice of envelope format reflects a tool’s priority between LLM compliance and human readability. XML envelopes are preferred for agentic tools that need reliable behavior; markdown dominates for developer-facing tools where humans will read and edit prompts directly.

See also: markdown-header-format, xml-vs-markdown-envelopes, format-interoperability

Sources

• [raw/prompts/articles/taxonomy-synthesis-2026-07-16.md]