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The llms.txt effect.

We HTTP-scanned 37,894 AI-cited domains from a corpus of 102,857. 5,035 have llms.txt. The two citation tests give different results, and neither shows what adding the file would cause.

Published
18 March 2026
Updated
4 September 2026
Sample
37,894 AI-cited domains
Window
1 January 2025 to 14 March 2026
Reading
5 minutes
lope.example/llms.txt

# Lope

> Running shoes for every mile. Guides, sizing and care.

## Guides

- [Choosing a daily trainer](https://lope.example/guides/daily-trainer)

- [Sizing and fit](https://lope.example/help/sizing)

## Shoes

- [Lope Daily](https://lope.example/shoes/daily): balanced, most miles

- [Lope Tempo](https://lope.example/shoes/tempo): firm and light

## Optional

- [Care and repairs](https://lope.example/help/care)

  1. 13.3%of 37,894 AI-cited domains publish one
  2. 89%of the files open with a title
  3. 79%score 4 of 4 on our file-quality rubric
  4. 6 KBmedian file size
Figure 1An llms.txt file, labelled. The file is an illustration; every rate comes from the 5,035 files we found in the scan.Jump to the findings

In short

Four findings, strongest first
  1. 13.3%

    of 37,894 AI-cited domains publish llms.txt. Among the 50 most-cited, it’s 6%.

    Figure 2
  2. p = 0.85

    for the top 5,000 cited domains: no significant citation difference between sites with and without the file.

    Figure 3
  3. 3 and 3

    median citations, with and without llms.txt. The means are 6.8 and 6.7.

    Figure 3
  4. 24.1%

    of SaaS and developer tool domains have one, against 1.5% of government and academic sites.

    Figure 4

The most-cited domains mostly skip it.

13.3% of the 37,894 AI-cited domains we scanned publish an llms.txt file. Among the 50 most-cited sites, only 6% do.

Move down the citation rankings and adoption rises, peaking at 16.1% in the top 5,000 before easing off across the long tail. That pattern doesn’t explain why sites adopt the file, or show any effect on citations.

Figure 2

The most-cited domains are the least likely to publish llms.txt

Share of domains with an llms.txt file, by citation rank

llms.txt adoption by citation tier
GroupValue
Top 50 (3 of 50)6%
Top 100 (7 of 100)7%
Top 250 (34 of 250)13.6%
Top 500 (72 of 500)14.4%
Top 1000 (153 of 1,000)15.3%
Top 2500 (398 of 2,500)15.9%
Top 5000 (803 of 5,000)16.1%
Top 10000 (1,571 of 10,000)15.7%
Top 25000 (3,424 of 25,000)13.7%
All scanned (5,035 of 37,894)13.3%
Source: Trakkr scan of AI-cited domains, 14 March 2026. Domains ranked by AI citation appearances; each tier includes the ones above it.Data

The two citation tests disagree.

The published snapshot reports averages of 6.8 citations with llms.txt and 6.7 without it, and the same median, 3. The top 5,000 most-cited domains return p = 0.85 in the Mann-Whitney U test, which isn’t statistically significant at the 0.05 level.

The full 37,894-domain sample returns p < 0.001, with a reported effect size of r = −0.065. That test is significant, while the effect is small. It must not be described as the same null result.

Figure 3

The same median, and two tests that disagree

Published citation medians for domains with and without the file, then the two cohort tests.

Median citations with and without llms.txt
Groupmedian citations
With llms.txt3
Without llms.txt3
Top 5,000 cited domainsMann-Whitney U. No statistically significant difference in this subset.
p = 0.85
Full sample, 37,894 domainsSignificant, with a small reported effect (r = −0.065). The JSON rounds this p-value to zero.
p < 0.001
Source: Trakkr scan of AI-cited domains, 14 March 2026. Means: 6.8 with the file, 6.7 without. The public data does not say which cohort these summaries describe.Data

Adoption follows the tech sector.

llms.txt adoption is led by SaaS and developer tools, at 24.1%. Government and academic sites sit at just 1.5%, while review sites and reference wikis are at 0%.

Uneven adoption leaves room for selection bias. The study doesn’t separate sector, site size, content quality or existing citation exposure from the decision to publish llms.txt.

Figure 4

Developer tools lead; reference and review sites have none

Share of scanned domains in each category with an llms.txt file.

llms.txt adoption by domain category
GroupValue
SaaS and Developer Tools (97 of 403 domains)24.1%
E-commerce (10 of 55 domains)18.2%
News and Media (52 of 332 domains)15.7%
Social Platforms (84 of 536 domains)15.7%
Government and Academic (9 of 581 domains)1.5%
Reference and Wiki (0 of 36 domains)0%
Review Sites (0 of 39 domains)0%
Source: Trakkr scan of AI-cited domains, 14 March 2026. Categories cover the named groups in the sample only.Data

Visibility scores look alike too.

Using Trakkr’s visibility score, which combines presence, rank, mentions and sentiment across AI models, brands with llms.txt have a median of 23.15 against 23.55 without it.

The medians are close. The comparison has no confidence intervals or adjusted causal estimate, so it can’t show that the difference is noise, or that llms.txt has no effect on recommendations.

Figure 5

Brands with and without the file score about the same

Trakkr visibility score, 0 to 100, for brands with both an audit and visibility reports.

Median visibilityWith llms.txt 23.1 · without 23.6

23.1with23.6without

Average visibilityWith llms.txt 27.8 · without 26.3

27.8with26.3without
Source: Trakkr visibility reports and site audits, 205 brands. Descriptive only: no confidence intervals or adjustment.Data

What this means.

Read these results as a dated observational snapshot, with separate tests for the full sample and its most-cited subset.

  1. Separate the two cohorts

    The top-5,000 test is not significant. The full-sample test is significant with a small reported effect. Reporting either result alone loses useful context.

  2. Association does not establish cause

    Sites choose whether to publish llms.txt. Sector, size, content and existing citation exposure may differ between groups. This study can’t isolate the effect of adding the file.

  3. The scan does not measure model behaviour

    Finding a file on a domain doesn’t tell us whether an AI system fetched or used it. Citation counts alone can’t separate training, search or retrieval.

  4. Measure the workflow you care about

    If you publish llms.txt for documentation or retrieval, test that workflow directly. A controlled or longitudinal study would be needed to estimate changes in citations.

How we ran it.

Everything you need to check our work, repeat it or cite it: who ran the study, when, on what data, and where it falls short.

Trakkr Research · Study 005

The llms.txt effect

Mack GrenfellFounder, Trakkr. Author and analyst.
Domains scanned
37,894from a corpus of 102,857 cited domains
With llms.txt
5,03513.3% of the scanned sample
Citations
337,362in 882 citation snapshots
Scanned
14 March 2026One dated, observational snapshot

Method

We ranked domains by how often AI answers cited them and scanned every domain with at least two appearances. An async HTTP check requested /llms.txt and validated the content, so HTML error pages, soft 404s and login redirects that return 200 don’t count as a file.

We then ran separate Mann-Whitney U tests, rather than t-tests, because citation counts are heavily right-skewed: one on the top 5,000 cited domains (p = 0.85) and one on the full sample (p < 0.001, r = −0.065). A separate descriptive comparison covers 205 brands with both site audits and visibility reports. Among adopters, 89% of files include a title, 98% contain URLs and 79% score 4 of 4 on the published rubric; those describe the files, not their effect.

Data

llmstxt_effect_stats.jsonAggregates only. No page or customer data.

Where it falls short

  • Not an experiment

    Sites choose whether to publish the file, so sector, size and content may differ between the groups.

  • Aggregates only

    No domain-level rows, confidence intervals or adjusted estimate are published, so the tests can’t be recomputed.

  • A selected sample

    These are AI-cited domains, not an estimate of adoption across the whole web.

  • No model behaviour

    Finding a file doesn’t show that an AI system fetched or used it.

Cite this study

Grenfell, M. (2026, March 18). The llms.txt effect (Trakkr Research Study 005). Trakkr. https://trakkr.ai/trakkr-research/llmstxt-effect

Questions,
answered.

The ones we hear most about this study.

This observational snapshot does not establish a causal citation benefit. The top 5,000 cited domains returned p=0.85; the full 37,894-domain sample returned p<0.001 with a small reported effect size, r=-0.065. These are different cohorts. A non-significant test does not prove no effect.

Ask anything about this studyAsk anything about this study

The Agent answers from our docs, methods and pricing, and links to the source.

AI crawler view

lope.example
llms.txtFound, 6 KB, 42 links
Crawler visitsGPTBot and ClaudeBot this week
Cited pages14 pages cited this month
Answer gaps3 questions with no pageFix drafted

Most-read by AI this week

/guides/daily-trainer      312 visits
/help/sizing               188 visits
/shoes/daily                97 visits

See what AI actually reads on your site.

Trakkr shows which AI crawlers visit, which pages they read and which ones get cited, then drafts the fixes for the gaps.