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About SerpPrism
SerpPrism is a small collection of SEO tools that run entirely in your browser.
Why these tools exist
Most SEO checking tools ask you to enter a URL, then crawl your site from their servers and show you a report. That is useful, but it means handing over an address you may not want logged, and waiting for a crawl you do not need if you only wanted to check one thing.
The tools here take the opposite approach: you paste the text or rules you want to check, and the analysis happens on your machine. There is no queue, no account, and no server-side record of what you checked.
What the tools deliberately do not do
They do not produce a site-wide SEO score. A single number cannot tell you which line of a robots.txt file is blocking a section, or which sentence of a paragraph is unreadable. Every tool here points at a specific thing instead, because that is what you can actually act on.
They also do not fetch live URLs. Browsers block cross-origin requests for good reasons, and a tool that worked around that would be a liability rather than a feature. If you need site-wide crawling, use a crawler — this site is for checking one thing quickly and privately.
Accuracy and limits
Where a measurement is approximate, the tool says so. The SERP preview measures rendered pixel width using the font stack and sizes Google uses on desktop results; it is accurate enough to tell you whether a snippet will be cut, and it is not a guarantee of what Google will display, because Google frequently rewrites descriptions using text from the page itself.
The robots.txt tester implements the longest-match rule from RFC 9309 including wildcards. It is not a substitute for Google's own tester in Search Console, which has access to Google's actual crawl behaviour — but it is much faster for answering "which of my rules is doing this?"
Who runs this
SerpPrism is built and maintained by Hongtao Ren (任宏涛), a developer based in Xi'an, China. He also builds JetBrains IDE plugins and a handful of small web tools; this is the one concerned with search results and page markup.
It started from a specific frustration. Every check that ought to take two seconds — does this snippet fit, is this path blocked, is this heading order sane — seemed to require pasting a URL into somebody else's server and waiting for a crawl. None of them actually need a server: a robots.txt rule can be evaluated in JavaScript, and a snippet's rendered width can be measured with a canvas. So these were built as plain client-side JavaScript instead.
What this site does and does not claim to know
Worth being straight about the limits. The tools implement published specifications — RFC 9309 for robots.txt, the Open Graph protocol, Google's documented hreflang behaviour — and each tool page states where a measurement is approximate rather than exact. Where behaviour is undocumented, or changes without notice, the page says so instead of guessing.
The guides are written from the same place: things you can check and fix in an afternoon, not strategic SEO advice. There is deliberately nothing here about link building, keyword research tooling or content calendars, because the useful version of that advice depends entirely on which site is asking.
Independence and money
SerpPrism is an independent site with no investors and no parent company. It is free to use and carries advertising; the advertising does not influence what any tool reports, because there is nothing in the code that could be influenced — the analysis runs on your machine and returns the same answer regardless.
Corrections
If a tool gives you the wrong answer, that is a bug and worth an email — use the contact page and include the input that produced it. Technical SEO advice also ages badly: several widely repeated claims were accurate five years ago and are not now. Being told which ones this site has repeated is genuinely useful.