Several online spellcheckers operate in a number of languages, including Spanish, and some of the easiest to access are Jspell.com and LanguageTool.org. Spanishchecker.com has an English input tool. If a professional program is required, Stilus has options in Spanish that include spelling, grammar and style checks.
Jspell.com offers spell checking in a range of languages as well as Spanish, and it also has a medical spell checker. It also checks word and character counts for text pasted into its checking screen. LanguageTool uses a similar copy and paste functionality, and it also provides grammar checks on the text provided. It is open source software that offers offline versions for OpenOffice and LibreOffice.
SpanishChecker is a site dedicated to Spanish spelling and grammar, but the interface operates in English. It does allow users to specify if they are native Spanish speakers and tailors feedback accordingly. For those who are prepared to pay for translation and checking services, Stilus offers a range of options, including a yearly subscription that allows instant proofreading of webpages in the chosen language.
An free extension is also available for the Chrome Web browser that operates a spell check function in 12 different languages, including Spanish. This allows users to write online with confidence.