Template Literal Engine

What this tool is used for

• Filling placeholders in a template with values to preview the result.
• Producing several variants of a message from one template.
• Checking a template for placeholders you forgot to supply.
• Generating a batch of strings from a template and a value list.
• Testing a template's output before wiring it into code.

Frequently Asked Questions

What placeholder syntax is recognised?

Exactly {{name}} where the name is word characters — letters, digits, underscore. That excludes three forms people carry over from Mustache and Handlebars: {{ name }} with spaces, {{first-name}} with a hyphen, and {{user.name}} dotted paths. Each is passed through verbatim rather than flagged.

What happens to a placeholder I leave blank?

It renders as an empty string, so the placeholder vanishes rather than showing a gap or raising an error. Mustache and Handlebars both treat a missing key the same way. Convenient for genuinely optional fields, and easy to miss when a field was simply forgotten — the Filled Placeholders counter is there for that.

Can a value contain template syntax itself?

It can, and it is never re-expanded: the template is scanned once, so a value holding {{other}} reaches the output literally. That rules out both recursive expansion and any infinite loop. Dollar patterns are literal too — a value of $& inserts those two characters rather than the matched text.

Is it safe to build SQL with this?

No. Values are substituted as raw text with no escaping or quoting, so a name containing an apostrophe breaks the SQL preset's quoting — and the same hole is an injection if that string ever reaches a database. Use this to draft the shape of a statement, and parameterised queries to execute one.

Why doesn't a shared link carry my filled values?

The template is held in the URL so a link reproduces it; the values are not, because they are usually the personal part — names, addresses, order numbers. Share the link to hand someone the template itself, and send the rendered output if what they need is the filled result.

Common errors and gotchas

• Leaving an unsubstituted placeholder in the output, which then ships as literal braces.
• Assuming the substitution escapes anything, which it does not — HTML or SQL context still needs handling.
• Using a placeholder name that appears inside a value, which then gets replaced too.
• Expecting nested placeholders to resolve, which a single pass does not do.
• Treating the engine as a template language, when it does substitution and nothing else.