HiddenContent.ai

HiddenContent.ai is an API that inspects a document before a model reads it and reports any text present in the file but invisible to a human looking at the page. Detection works by resolving style inheritance to establish per-run visibility, rendering the page, and comparing the rendered ink against the file contents. Because it compares rather than pattern matches, it catches implicit injections that carry no instruction wording at all, which is how most of them are written. Coverage includes white-on-white and near-invisible text, sub-point font sizes, text layered behind images or moved off the printable area, custom number formats that blank a spreadsheet cell while preserving its value, alternate content fallbacks Word never renders, speaker notes, and zero-width characters. PDF, DOCX, XLSX, PPTX and the legacy binary formats are parsed natively. Every finding returns a page or cell location, the concealment technique, a verdict separating carelessness from deliberate attack, clean text for your pipeline, and a certificate that verifies offline. No third-party APIs, no model inference and no file egress, with a self-hosted build available. Prepaid at one cent per page.