URL: /rules/crawl/sitemap-lastmod-drift

---
title: "Sitemap Lastmod Drift"
description: "Checks that sitemap lastmod matches the page's own dateModified"
---

Checks that sitemap lastmod matches the page's own dateModified

| | |
|---|---|
| **Rule ID** | `crawl/sitemap-lastmod-drift` |
| **Category** | [Crawlability](/rules/crawl) |
| **Scope** | Site-wide |
| **Severity** | warning |
| **Weight** | 4/10 |

## What it checks

For every crawled page that appears in a sitemap with a `lastmod`, the rule compares that
`lastmod` against the page's own strongest date signal: schema.org `dateModified`, else the
`dateModified`-equivalent markup (`[itemprop="dateModified"]` meta / `<time>`), else the visible
published date. Pages with no date signal at all are skipped: that is
[Content Freshness](/rules/content/freshness) territory, not drift.

The two directions are reported as separate checks, because they point at different code:

| Check | Fires when | Usual cause |
|-------|-----------|-------------|
| `sitemap-lastmod-behind-page` | `lastmod` is older than the page's `dateModified` by more than 7 days | Stale cached sitemap, or a generator resolving `publishedAt ?? updatedAt` while the page renders `updatedAt ?? publishedAt` |
| `sitemap-lastmod-ahead-of-page` | `lastmod` is newer than the page's `dateModified` by more than 30 days | `lastmod` stamped at build/deploy time instead of on content change |

Each finding reports both dates and the gap in days. Same-day and within-threshold differences
never warn.

Lastmod being *older* than the page's own `dateModified` is the more clearly wrong of the two:
it tells crawlers not to bother re-fetching a page that has in fact changed.

## Solution

A sitemap lastmod that disagrees with the page's own dateModified points at the sitemap generator, not the content. Lastmod OLDER than the page's dateModified tells crawlers not to bother with a page that has in fact changed - usually a stale cached sitemap, or a generator resolving `publishedAt ?? updatedAt` while the page renders `updatedAt ?? publishedAt` (a precedence inversion; both fields are present, so presence checks pass). Lastmod NEWER than the page's dateModified usually means lastmod is stamped at build/deploy time. Drive both values from the same content-modification timestamp.

## Options

This rule supports the following configuration options:

| Option | Type | Default | Description |
|--------|------|---------|-------------|
| `ahead_days` | number | `30` | Days a sitemap lastmod may run ahead of the page's own dateModified before warning |
| `behind_days` | number | `7` | Days a sitemap lastmod may lag the page's own dateModified before warning |

### Configuration Example

```toml squirrel.toml
[rules."crawl/sitemap-lastmod-drift"]
ahead_days = 30
behind_days = 7
```

## Enable / Disable

### Disable this rule

```toml squirrel.toml
[rules]
disable = ["crawl/sitemap-lastmod-drift"]
```

### Disable all Crawlability rules

```toml squirrel.toml
[rules]
disable = ["crawl/*"]
```

### Enable only this rule

```toml squirrel.toml
[rules]
enable = ["crawl/sitemap-lastmod-drift"]
disable = ["*"]
```