Rule Frontmatter

Passthrough

• Tessl preserves rule file frontmatter byte-identical from publish to install — no per-agent translation, no field filtering
• Whatever frontmatter the source rule contains reaches every consuming agent's context
• The agent's model reads the frontmatter and applies the rule according to its declared scope
• Verified: a published rule scoped to TypeScript fires on TS files and skips Python files

Always-On Rules

• For rules that apply regardless of file or task context (commits, secrets, code formatting, error handling): set alwaysApply: true in the rule file frontmatter
• Omit applyTo: — the rule has no narrowed scope
• description: is optional for always-on rules; add it when the README rules-table row needs a complement, otherwise the rule body's H1 + sections speak for themselves

Conditional Rules

• For rules whose prescriptions only fire in specific files or contexts: set alwaysApply: false in the rule file frontmatter and add applyTo:
• applyTo: syntax is "<glob list> — <natural-language clause>" — both halves required. Example: applyTo: "skills/**/SKILL.md — when authoring or modifying skills"
• The em dash separates the file-level scope (globs) from the action-level scope (prose); the model reads both halves and narrows on whichever signal is clearer
• globs: and paths: are accepted field-name aliases for applyTo: — the value still follows the em-dash glob+prose form; pick one field name per file
• description: is a rule summary, not a scoping mechanism — never put scope prose only in description: as a substitute for applyTo: on a conditional rule

When to Path-Scope

• Path-scope when every prescription in the rule is bound to a specific file set or context (plugin-authoring rules whose content only fires inside rules/, skills/, evals/ are good candidates)
• Stay universal when the rule mixes file-bound and broad guidance — applyTo: is exclusionary at the model layer, so a too-narrow scope drops the broad bits
• Example — dependency-management covers two practices:
  • "stdlib first" fires when writing code
  • "pin versions" fires when editing manifests
• Scoping dependency-management to manifests would silently drop the code-level guidance, so the rule stays universal

Frontmatter Is the Only Scope Surface

• alwaysApply and applyTo: live only in the rule file frontmatter — .tessl-plugin/plugin.json lists rule paths in its rules array and carries no per-rule config
• Install-time write map per agent — docs/tessl-rule-frontmatter.md is the repo-internal draft of additions for docs.tessl.io. The docs/ directory is .tesslignored and does not ship with the published plugin, so consumers read the integrated content on docs.tessl.io once it lands; until then, read the source on GitHub