60 AI-written WordPress plugins, and JavaScript escaping that is safe by accident

This post has two halves: what "escape your output" actually means once the obvious answer stops working, and then a study of whether current AI assistants get that harder version right. It continues a series on what coding assistants actually produce when a non-expert asks them for WordPress code. Start with a line that passes review and still leaves a hole: echo '<a href="' . esc_html ( $url ) . '">Visit</a>' ; There is an escaping function wrapped around the value. A grep for esc_ finds it. A quick review passes it. Now set $url to javascript:alert(document.cookie) . The link still runs when the visitor clicks it. esc_html() escapes characters that matter in HTML text, like < and > . It does nothing about a dangerous URL scheme. The code is escaped. It is escaped for the wrong context. From the outside, correct escaping and wrong-context escaping look identical. A URL is a different context and needs its own escaper. That escaper is esc_url() , and it returns an empty string for a javascript: URL. Which escaper goes where Escaping is context-dependent. "Sanitize on input, escape on output" is the rule the first post of this series covers, but "escape on output" hides a second decision: which escaper. The answer depends on where the value lands on the page. Where the value lands Escaper Visible text between tags ( <p>HERE</p> ) esc_html() Inside an attribute ( title="HERE" ) esc_attr() A URL slot ( href="HERE" , src="HERE" ) esc_url() , which also enforces a safe scheme Inside a tag attribute that holds JavaScript ( onclick="greet('HERE')" ) esc_js() , scoped to this slot by core's own documentation Any value handed to JavaScript inside a <script> block ( var data = HERE ) wp_json_encode() , which writes its own quotes; add JSON_HEX_TAG when the value is untrusted HTML you want to keep, like a formatted post body wp_kses() with an explicit allow-list Six functions, one job each. The mistake is almost never "forgot to escape". It is "escaped for the wrong context",