Assert String Present in HTML
Verify that specific text appears in the rendered page.
The Problem
Sometimes you need a simple sanity check: does the page actually contain the city name, the product title, or the disclaimer text? This assertion searches the full HTML for a case-insensitive substring match.
The Hard Way
Ctrl+F in the browser. For one page. Now multiply by every city in your database and every weekly deployment.
The SEODiff Way
One API call. Results in under 2 seconds.
POST https://seodiff.io/api/v1/agent/evaluate
{"urls": ["https://example.com/city/springfield"], "assertions": [{"rule": "contains_string", "value": "Springfield"}]}| Parameter | Type | Example |
|---|---|---|
value | string | Springfield |
Code Examples
Copy-paste examples in your preferred language:
cURL
See the full evaluation example in cURL →
Python
See the full evaluation example in Python →
Node.js
See the full evaluation example in Node.js →
Go
See the full evaluation example in Go →
PHP
See the full evaluation example in PHP →
Related Assertions
not_contains_string
Ensure specific text does NOT appear in the rendered page.
regex_match
Verify that a regex pattern matches somewhere in the page HTML.
no_placeholders
Find template variables like {{city}} or [TBD] that leaked into production HTML.
Use in CI/CD
Add this assertion to your deployment pipeline. Works with any CI platform:
🐙 GitHub Actions
Block bad deployments with automated SEO checks in your GitHub Actions CI/CD pipeline.
🦊 GitLab CI
Add automated SEO quality gates to your GitLab CI/CD pipelines.
▲ Vercel
Automatically validate SEO on every Vercel preview deployment before promoting to production.