Knap: a data-to-Markdown template language from the Obsidian team

The problem Knap solves, and the two products it already runs inside

Most template engines assume the output is HTML and the threat model is a developer writing the template. Knap assumes the output is Markdown and the template may come from somewhere else. The README states that it powers templating in Obsidian Web Clipper and Obsidian Importer, which are two separate cases of the same job: take a page or a file, extract fields, and write a note. A clipper needs a title, a URL, an author and a date turned into frontmatter and a body. An importer needs to map a foreign structure onto the same shape.

The audience is therefore narrower than "anyone who needs templates". It is developers embedding a template step in an application that hands templates to users, and people who want to run that step from a shell. If you are writing a static site generator, the Markdown focus is a constraint rather than a feature, and the syntax is small on purpose.

How Knap works: parse to an AST, interpret without eval

The README is explicit about the mechanism: Knap parses templates into an AST and interprets them without eval or arbitrary JavaScript execution. That single sentence explains most of the design. A template is data, not code. The interpreter walks the tree and resolves variables against a context the host supplies.

That context is the second half of the design. The README says applications control the data and integrations available to templates. So the engine does not reach into a global scope on its own; whatever a template can see, the embedding application put there. Filters are supplied the same way. The library example passes standardFilters into createEngine, which means the filter set is a parameter, not a built-in constant. If you want a template to have no filters at all, the API allows that.

The output is Markdown, and the repository also exposes an html entry point alongside prism, codemirror and highlightjs adapters. Those are for editing and highlighting templates in other tools, not for changing what the engine emits.

Installing Knap and rendering a first note from JSON

The package installs from npm. The README notes that Node.js 20 or later is required for the CLI, so check that before anything else.

npm install knap

The CLI renders a template file against a JSON data file and writes the result. This is the exact invocation the README gives.

npx knap render template.md --data data.json --output note.md

After it runs, note.md holds the rendered Markdown. The README also mentions inline templates, validation, batch rendering, CSV input and offline language help, all documented in the CLI guide rather than in the README itself.

From a script, the library path is createEngine plus a render call. The README uses renderOrThrow, which throws on failure instead of returning a result object, and the template below is the one it shows.

import { createEngine, standardFilters } from 'knap';

const engine = createEngine({ filters: standardFilters });

const markdown = await engine.renderOrThrow(
	'# {{ title | trim }}\n\n{{ tags | list }}',
	{
		variables: {
			title: '  An imported note  ',
			tags: ['reference', 'reading'],
		},
	},
);

The trim filter strips the surrounding spaces from the title, and list renders the array. The API guide covers rendering, validation, custom filters, asynchronous variables, HTML filters and execution limits.

The limit that matters: no eval is a security choice with a cost

Removing eval removes a class of risk, and it also removes a class of capability. A template cannot call a function you did not expose, cannot import a module, and cannot compute anything the filter set does not already provide. If your users ask for a filter that transforms a date in a way standardFilters does not cover, the answer is a new filter in the host application, not a line in the template.

The README points to execution limits in the API guide, which implies unbounded templates are a recognised concern, but the README does not state what those limits are or what the defaults are. That is the first thing to check in the source before putting Knap behind a user-supplied template box. The same applies to asynchronous variables: they are documented in the API guide, and the README gives no example, so anyone relying on them is reading the guide, not the front page.

Knap is also the wrong tool outside its lane. It emits Markdown. If you need HTML with escaping semantics tuned for a browser, or a template language whose ecosystem already has a decade of Stack Overflow answers, the small surface here works against you.

Knap compared with a general-purpose template engine

The obvious comparison is a JavaScript template engine in the Mustache or Handlebars family. The difference is where the trust boundary sits. Those engines typically evaluate a template against a data object and let the template author reach whatever the object graph exposes, with helpers registered globally or per render. Knap inverts the default: the README states that applications control the data and integrations available, and the engine never executes JavaScript. So a Knap template is closer to a query than to a program.

That has a practical consequence for validation. Because the template is an AST, the engine can validate it without rendering, which is why the README lists validation as a CLI capability and the API guide covers it as a library one. A Mustache-style engine generally finds out that a template is malformed when it runs. For a clipper that stores user templates and applies them later, checking a template at save time is a different product experience from discovering the problem at capture time.

The trade is expressiveness. Anything that requires real computation belongs in the host application, exposed as a filter or a variable. Teams that expect to write logic in the template will find the ceiling quickly.

Licence, releases and what maintenance looks like

Knap is MIT licensed, and the LICENSE file sits at the repository root. For most adopters that means the usual MIT obligations: keep the copyright notice and the permission notice with copies or substantial portions of the software. It does not mean the project offers support, and it does not mean the name can be used to endorse a derivative. That is a description of the licence text, not legal advice; if the distinction matters to your organisation, read LICENSE and talk to counsel.

The repository is not archived, and the last push was on 2026-09-15. Releases are frequent and small: 0.5.0 on 2026-09-13, 0.5.1 on 2026-09-14, 0.6.0 on 2026-09-14. The version is still 0.x, so the API guide is the contract and semver's stability promises do not apply in the way they do at 1.0. The CHANGELOG.md at the root is where breaking changes would appear, and it is worth reading before an upgrade rather than after.

Upgrade cost is low if you use the documented surface: createEngine, standardFilters, renderOrThrow. It rises if you depend on the adapter entry points, since prism, codemirror and highlightjs each have their own peer packages and their own version constraints.

Editorial conclusion

Adopt Knap if you are generating Markdown from structured data and want templates that cannot execute arbitrary JavaScript, since the parser builds an AST and the host application decides which variables and integrations templates can reach. Skip it if you need a general-purpose templating language for HTML, or if you cannot run Node.js 20 or later for the CLI. Before committing, verify two things in the source: which filters ship in standardFilters, and what execution limits the API guide documents, because those two decisions determine whether a template can loop forever or reach data you did not intend to expose.

Frequently asked questions

Official sources

1. License: MIT
2. obsidianmd/knap on GitHub
3. Project website
4. README
5. Releases