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.
One caveat on method: Rank Math emits no front-end output until its wizard is finished or skipped, so in the benchmark run we applied only what its Skip button sets, while Slim SEO needed nothing. Hydrogen SEO, which we make, is not part of this comparison.
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
Only The SEO Framework rivals Slim SEO for lightness in this 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. Slim SEO's autoloaded options actually measured a hair under the no-plugin baseline; Rank Math's grew by 11.6 KB and most of that stayed after deactivation. Slim SEO released everything.
In wp-admin, Rank Math added two menus and a 1,792 KB editor payload; Slim SEO added no menu entries and 187.7 KB. Slim SEO also starts printing tags the moment you activate it, while Rank Math stays silent on the front end until someone completes or skips its wizard.
Output is more even than cost. Slim SEO's schema graph was the bigger one, 10 JSON-LD types (3,828 bytes) to Rank Math's 6 (2,665 bytes). 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 10 schema types and the 40 featured images listed in your sitemap out of the box.
- You want a plugin that adds no admin menus and needs no setup.
- You want everything released when you deactivate it.
Switching between them
Rank Math data can come across through Slim SEO's own migration tool, and Rank Math's wizard imports from several other plugins; the current source lists are in each plugin's documentation. Expect most of Rank Math's module settings to have no home in Slim SEO, which has very few options, so what you really need to verify afterwards is per-post titles, descriptions and redirects. Hydrogen SEO reads Rank Math and Slim SEO data too, previews the whole import before writing and keeps an Undo; the steps are in moving your SEO data to Hydrogen SEO.
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.