templ

A templ template is a rendering function, not a program. Three biases decide most calls:

• Compute in Go, render in templ. Every transformation, validation, and I/O call belongs in a Go function that hands the template a finished value.
• Escaping is automatic inside .templ source and nowhere else. Every bypass carries a named API, and reaching for one is a decision to emit unchecked output.
• .templ source and the generated *_templ.go are one artifact. Neither is correct without the other.

Syntax

• { } writes a value; {{ }} runs Go statements. html/template gives {{ }} the opposite job, and that habit carries over silently.
• { } accepts string, the numeric types, bool, and any type defined on them. Convert anything else with fmt.Sprintf first.
• An expression returning (T, error) propagates its error out of Render, with the source location attached.
• Close every tag in the source, void elements included — <br/>, <img src="x"/>. templ strips the / from void elements in the output, so the source form and the rendered form differ by design.
• Text starting with if, for, or switch parses as a statement. Wrap it as an expression — { "if you must" } — or capitalize the keyword.
• A comment inside a templ block is an HTML comment and reaches the output. // and /* */ work only outside a templ block, and HTML comments do not nest.
• Bind an expensive call to a {{ }} variable rather than repeating it across two { } expressions.

Read [${CLAUDE_SKILL_DIR}/references/syntax.md] when templ generate reports a parse error, or when writing the first template in a package — it carries the file layout, every control-flow form, and the escaping behavior with rendered output.

Components

• A component can write part of its output before it returns an error. Render into a bytes.Buffer and copy on success where the response must be all-or-nothing.
• A code-only component escapes nothing on its own. Wrap every interpolated value in templ.EscapeString, because templ.ComponentFunc writes exactly the bytes handed to it.
• Declare every templ.NewOnceHandle() at package level. @templ.NewOnceHandle().Once() written inline builds a fresh handle per call, so the guarded content renders every time.
• Wrap a once-guarded asset shared across packages in an exported component. The handle is package state and cannot be shared any other way.
• A fragment suppresses output, not work. templ.WithFragments and templ.RenderFragments execute the whole template and write only the named fragment.
• { children... } renders the block a caller passed as @component() { ... }. A code-only component reads the same block from the context with templ.GetChildren.