Rank Math vs Slim SEO: every switch against almost none
Slim SEO costs a fraction of Rank Math: +10.0 ms and 2 queries per request against +36.1 ms and 16, no tables against six, and a 1.4 MB package against 15.1 MB. Rank Math is ahead on social tags, especially X cards, and on sitemap lastmod, and it gives you far more to configure.
We measured both in our seven-plugin benchmark, free versions at defaults on one WordPress 7.1 install. We build Hydrogen SEO, which is not in this pair.
The numbers
| Measured | Rank Math 1.0.278 | Slim SEO 4.10.1 |
|---|---|---|
| Front-end PHP time added | +36.1 ms | +10 ms |
| Peak memory added | +8.5 MB | +2 MB |
| Database queries added | +16 | +2 |
| Hooks registered | +155 | +51 |
<head> bytes added | +4,965 | +1,649 |
| Meta description by default | Yes | Yes |
| JSON-LD types printed | 6 | 10 |
| Open Graph / X tags | 11 / 8 | 11 / 2 |
| Sitemap URLs listed | 59 | 73 |
| Sitemap image entries | 0 | 40 |
lastmod coverage | 59 / 59 | 50 / 73 |
| Custom database tables | 6 | 0 |
| Autoloaded options added | +11.6 KB | -0.2 KB |
| Plugin package size | 15.1 MB | 1.4 MB |
| Block editor assets | 24 files, 1,792 KB | 14 files, 187.7 KB |
| After deactivation | +11.0 KB still autoloading | Releases everything |
Measured on one WordPress 7.1 install (PHP 8.2, MySQL 8.0, Twenty Twenty-Five, 40 posts), each plugin alone with default settings, against a no-plugin baseline. Bold marks the better number in each row. Full method: how we tested.
What the numbers mean
Slim SEO is one of the two lightest plugins in the test. Memory grew by +2.0 MB against Rank Math's +8.5 MB, hooks by 51 against 155, <head> by 1,649 bytes (the smallest in the field) against 4,965. Its autoloaded options came out fractionally below baseline; Rank Math's grew by 11.6 KB and most of that stayed after deactivation. Slim SEO released everything.
In wp-admin, Slim SEO added no menu items at all and loaded 187.7 KB into the editor. Rank Math added two menus and loaded 1,792 KB. Slim SEO also works immediately on activation, while Rank Math prints nothing until its setup wizard is completed or skipped.
Output is more even than cost. Slim SEO printed more schema: 10 JSON-LD types in 3,828 bytes against Rank Math's 6 in 2,665. Its sitemap was fuller too: 73 URLs including archives and all 40 featured images, where Rank Math listed 59 URLs and no images at defaults. Rank Math wins on sitemap freshness, stamping lastmod on every URL where Slim SEO left 23 of 73 unstamped. And Rank Math wins social tags clearly: 11 Open Graph and 8 X against Slim SEO's 11 and 2. If X share cards matter to your traffic, that gap is real.
The underlying choice is about control. Rank Math is one of the most configurable free SEO plugins, which suits people who want to tune everything. Slim SEO has almost no configuration surface by design; you install it and it runs. Neither approach is wrong, but they suit very different owners.
Choose Rank Math if
- You want full X card output (8 tags against 2).
- You want
lastmodon every sitemap URL. - You want many settings and modules in the free plugin.
- You are happy to finish the setup wizard and audit settings.
Choose Slim SEO if
- You want a tiny footprint: +10.0 ms, no tables, 1.4 MB package.
- You want more schema (10 types) and featured images in the sitemap at defaults.
- You want a plugin that adds no admin menus and needs no setup.
- You want everything released when you deactivate it.
Switching between them
Slim SEO includes a migration tool that can import from Rank Math, and Rank Math's wizard can import from several other plugins; check each plugin's documentation for the current source list. Because Slim SEO has so few settings, most of Rank Math's configuration simply has nowhere to go, so check per-post titles, descriptions and redirects afterwards. Hydrogen SEO imports from both with a dry run and an Undo; see switch from another SEO plugin.
Common questions
Is Slim SEO faster than Rank Math?
Yes: +10.0 ms and 2 queries against +36.1 ms and 16 queries in our benchmark. Slim SEO creates no tables; Rank Math creates six.
Which has better social tags?
Rank Math. Both printed 11 Open Graph tags, but Rank Math printed 8 X tags against Slim SEO's 2.
Which sitemap is more complete?
Slim SEO's had more: 73 URLs and 40 images against 59 and none. Rank Math's had lastmod on every URL; Slim SEO's had it on 50 of 73.