# i requested page.md.md and wondered why it returned 404

> a simple bug caused me to request `page.md.md` instead of `page.md`. here's why url normalization is critical.

a bug that cost hours to debug. the symptom: `404` for urls that should've worked. the cause: double extensions. `page.md.md` instead of `page.md`.

## appending .md to a path that already had it

my acquisition ladder constructs `.md` urls by appending `.md` to the path:

```
base url: /docs/getting-started
.md url: /docs/getting-started.md
```

but some sites already had `.md` in their canonical urls:

```
base url: /docs/getting-started.md
.md url: /docs/getting-started.md.md
```

double extension. `404`. extraction fails.

## how it happened

naive implementation:
```javascript
const mdUrl = `${url}.md`
```

if `url` is `/docs/page`, this works: `/docs/page.md`.
if `url` is `/docs/page.md` (already has extension), this becomes `/docs/page.md.md`.

sites where this happened:
- sites that expose `.md` directly in their canonical paths
- some docusaurus configurations
- sites with custom routing that includes `.md`

## normalize the extension before adding .md

normalize before constructing:

```javascript
function normalizeExtensions(url) {
  // strip trailing extensions
  return url
    .replace(/\.mdx?$/, '')    // remove .md and .mdx
    .replace(/\.html?$/, '')   // remove .html and .htm
}

const mdUrl = `${normalizeExtensions(url)}.md`
```

simple. but critical.

## other extension issues

it's not just `.md.md`:

- `.html.html`
- `.mdx.md` (site uses `.mdx`, i append `.md`)
- `.php.md`

any site that includes extensions in canonical paths needs normalization.

## strip the existing extension before constructing a url

before constructing any url with a known extension, strip existing extensions first.

```javascript
// bad
const newUrl = `${url}.md`

// good
const baseUrl = stripExtensions(url)
const newUrl = `${baseUrl}.md`
```

## testing for edge cases

url normalization is full of edge cases:

- query strings: `/docs/page?ref=nav` → `/docs/page.md?ref=nav`
- anchors: `/docs/page#section` → `/docs/page.md#section`
- trailing slashes: `/docs/page/` → `/docs/page.md`

each of these needs careful handling.

## test url construction against real docs paths

url normalization sounds simple. it's not.

tiny bugs in url construction cause extraction failures that are hard to debug. always normalize. always test with real urls.

---

**related:**
- [how i probe docs endpoints](/blog/acquisition-ladder)
- [html extraction](/blog/html-to-markdown-extraction)