Sitemap Index

A sitemap index is a sitemap of sitemaps — how large sites split past the 50,000-URL limit, how many URLs you can cover, and the splitting strategy that actually pays off.

First published: Jun 22, 2026 · Last updated: Jul 18, 2026 · Advanced
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A sitemap index is a sitemap of sitemaps: a single file that lists your other sitemap files instead of listing URLs. You need one once a single sitemap would exceed 50,000 URLs or 50MB uncompressed, or when you want to organize a large multi-section/region site. An index can reference up to 50,000 child sitemaps, each holding up to 50,000 URLs — so one index covers 2.5 billion URLs, and the 500-index-per-site limit in Search Console puts the theoretical ceiling at 1.25 trillion. You'll never run out of capacity. Children live on the same site at the same directory level or lower, you don't nest an index inside an index, and you submit only the index. The real payoff is splitting by section or content type so you can read submitted-vs-indexed per segment in Search Console.

TL;DR — A sitemapA sitemap is a file that lists the pages, images, videos, and other files on your site so search engines can discover them. It helps discovery, but submitting a sitemap doesn't guarantee crawling or indexing. indexStoring a crawled page in the search index so it can appear in results. Crawled is not the same as indexed — Google selects what to keep, and indexing isn't guaranteed. is a sitemapA sitemap is a file that lists the pages, images, videos, and other files on your site so search engines can discover them. It helps discovery, but submitting a sitemap doesn't guarantee crawling or indexing. of sitemaps — a <sitemapindex> file listing <sitemap> entries (<loc> + optional <lastmod>) instead of URLs. You need one once a single sitemap would exceed 50,000 URLs or 50MB uncompressed, or to organize a large multi-section/region site. An index can reference up to 50,000 child sitemaps × 50,000 URLs each = 2.5 billion URLs per index; with up to 500 index files per site in Search ConsoleA free Google service that reports how a site performs in Google Search and surfaces problems with how Google crawls, indexes, and serves it. It's first-party data straight from Google — but you don't need it to appear in results., the theoretical ceiling is 1.25 trillion — a number no real site approaches. Children stay on the same site at the same directory level or lower, you don’t nest an index inside an index (no tag for it, no tooling support), and you submit only the index. The payoff worth chasing: split by section/content type so you can read submitted-vs-indexed per segment.

What a sitemap index file actually is

A sitemap indexA sitemap index is a sitemap of sitemaps — a single file that lists your other sitemap files instead of listing URLs directly. It's how large sites stay under the 50,000-URL / 50MB-per-sitemap limit while submitting just one file. is a sitemap whose entries are other sitemaps. Where a regular sitemap wraps <url> blocks in a <urlset>, an index wraps <sitemap> blocks in a <sitemapindex>. Each <sitemap> has a <loc> pointing at one of your sitemap files and, optionally, a <lastmod>. That’s the whole structure — it carries no page URLs of its own. Evidence for this claim A sitemap index contains sitemap entries with a required loc value and an optional lastmod value. Scope: Sitemaps.org protocol structure for sitemap index files. Confidence: high · Verified: Sitemaps.org: Sitemap index XML tag definitions

It exists for one reason: the sitemaps format has hard size limits, and big sites blow past them. So you split your URLs across many sitemaps and use an index to present them to search engines as a single unit.

When you need one

Two triggers:

  1. You hit the size limits. A single sitemap maxes out at 50,000 URLs or 50MB uncompressed, whichever comes first. Google’s guidance is direct: “If you have a sitemap that exceeds the size limits, you’ll need to split up your large sitemap into multiple sitemaps.” Evidence for this claim A sitemap index can list up to 50,000 sitemap files, and each sitemap is limited to 50,000 URLs or 50 MB uncompressed. Scope: Google-supported sitemap and sitemap-index limits. Confidence: high · Verified: Google Search Central: Manage sitemaps with a sitemap index file Once you’ve split, an index ties the pieces together.
  2. You want to organize a large site — even under the limit. Multi-section sites (blog vs. products vs. category pages) and multi-region/multi-language sites are far easier to manage and monitor as separate sitemaps under one index. That organizational use is, in my view, the better reason to reach for an index, and I come back to it in the Frameworks tab.

Anatomy

The index is small and dull by design — <sitemapindex>, then a <sitemap> block per child, each with a <loc> and an optional <lastmod>:

<?xml version="1.0" encoding="UTF-8"?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <sitemap>
    <loc>https://www.example.com/sitemap1.xml.gz</loc>
    <lastmod>2024-08-15</lastmod>
  </sitemap>
  <sitemap>
    <loc>https://www.example.com/sitemap2.xml.gz</loc>
    <lastmod>2024-08-15</lastmod>
  </sitemap>
</sitemapindex>

Notes that matter:

  • The namespace is the same sitemaps.org/schemas/sitemap/0.9 you use on a regular sitemap; the file is UTF-8 and <loc> values are fully-qualified absolute URLs.
  • Children can be gzipped — .xml.gz is fine, and the 50MB cap is measured on the uncompressed size.
  • The optional <lastmod> here describes when that child sitemap last changed, not when individual pages changed.

How many can you submit — and how many pages is that?

This is where people lowball the ceiling. Stack the limits up:

  • Google Search ConsoleA free Google service that reports how a site performs in Google Search and surfaces problems with how Google crawls, indexes, and serves it. It's first-party data straight from Google — but you don't need it to appear in results. accepts up to 500 sitemap index files per site: “You can submit up to 500 sitemap index files for each site in your Search ConsoleGoogle's free tool for monitoring crawling, indexing, and search performance. account.”
  • Each index can list up to 50,000 child sitemaps.
  • Each child sitemap can hold up to 50,000 URLs.

Do the multiplication and the theoretical ceiling is 500 × 50,000 × 50,000 = 1.25 trillion URLs (1,250,000,000,000). Treat that as a ceiling no real site approaches, not a target — the takeaway is simply that you will never run out of sitemap capacity. And you rarely need to get fancy with multiple index files at all: a single sitemap index, without submitting any others, already covers 50,000 × 50,000 = 2.5 billion URLs. If you’ve got 2.5 billion indexable URLs, your sitemap setup is not your problem.

Location rules

The child sitemaps an index references have to live on the same site as the index, and at the same directory level or lower than the index file. An index at https://www.example.com/sitemap-index.xml can point at https://www.example.com/sitemaps/products.xml, but not at a sitemap on a different host or sitting above its own path. Break this and Search Console flags the children as “URL not allowed.” (Cross-domain references are only valid when both domains are verified in Search Console — but for an ordinary single-site index you don’t go there.)

Don’t nest an index inside an index

A sitemap index lists sitemaps, not other indexes. Neither sitemaps.org’s live protocol page nor Google’s sitemap-index documentation states this in so many words today — I checked both directly rather than trust an older paraphrase. What the protocol does say is narrower: the <loc> tag inside a <sitemapindex> is defined as identifying “a Sitemap, an AtomAn RSS or Atom feed is an XML file listing a site's most recently published or updated URLs. Search engines accept it as a sitemap-style discovery signal for fresh content — not a replacement for a full XML sitemap. file, RSS file or a simple text file” — an index file isn’t on that list, and the format has no tag for nesting one index under another. Every sitemap generator, plugin, and search engine I’m aware of treats index-of-indexes as unsupported on that basis; it’s a strong practitioner convention grounded in the format’s structure rather than a single quotable sentence from either doc. Treat it as a hard rule: one level of indexingStoring a crawled page in the search index so it can appear in results. Crawled is not the same as indexed — Google selects what to keep, and indexing isn't guaranteed. only. If you find yourself wanting an index-of-indexes, you almost certainly have room to reorganize within the 2.5-billion-URL ceiling a single index already gives you.

TIP

Check the index structure and child locations before submission with the XML Sitemap Validator Free

  1. Paste the sitemap index XML or fetch its deployed URL.
  2. Fix nested indexes and child entries that violate host or directory rules.
  3. Validate again, then submit the one clean index and monitor child fetch status in Search Console.
A sitemap index cannot contain another index. Flatten the structure so the submitted index points directly to URL sitemaps.

The completed XML Sitemap Validator result reports that a sitemap index contains another sitemap index and recommends referencing URL sitemaps directly instead.

Submit only the index

You submit the index file, and that single submission pulls in every child sitemap it references — you don’t need to submit the children one by one. John Mueller put it plainly: “You can submit the individual ones, but you don’t really need to.” Submitting both the index and its children isn’t harmful, just redundant. One clean submission of the index is the move.

That said, submitting a sitemap — index or not — is a discovery aid, not an indexing guarantee. The index helps engines find your sitemaps; it doesn’t promise the URLs inside them get crawled or indexed.

Splitting strategy — for reporting, not crawl efficiency

Here’s the part that’s underplayed everywhere else. How you split your sitemaps across an index does not change how Google crawls or indexes your pages. The reason to split thoughtfully is monitoring. Mueller’s framing is the one I lean on: “I generally recommend splitting a sitemap file into logical parts of your site so that you can monitor those parts individually (eg, category pages vs detail pages…). … It doesn’t change how Google crawls & indexes them, it’s really just so that you can track them better on your side.”

The practical payoff: the Search Console Sitemaps reportThe Google Search Console report where you submit sitemaps and watch how Google processes them — type, last read date, status, and how many URLs were discovered. It confirms Google read your list; it doesn't prove anything got indexed. shows submitted-vs-indexed counts per sitemap. Split your index by section or content type — blog, products, categories, docs, per region — and you can see which segment is under-indexed instead of staring at one site-wide number. That’s a diagnostic I use constantly. (It’s the same reason I’ll keep a sitemap of old URLs around during a migration: so I can watch that specific set drop out of the index in GSC.)

So split by what you want to measure, not by some imagined crawl benefit. The crawl benefit isn’t there; the reporting benefit is real.

How it relates to the rest of the sitemap family

A sitemap index sits on top of your regular XML sitemapsAn XML sitemap is a UTF-8 file listing the canonical URLs on your site (with optional lastmod) so search engines can discover and prioritize them. It's a discovery and diagnostic aid, not a guarantee of indexing — and Google ignores its priority and changefreq tags., and the broader sitemaps overview is the place to start if you’re new to the whole topic. Your image and video sitemaps are just more child files an index can reference, and the whole apparatus is part of how search engines handle discovery. None of those need linking out from here — they’re siblings in the same cluster.

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