How to Prevent Prompt Injection: 13 Attacks, Tested
The article describes testing 13 self-written and 12 model-written prompt injection attacks against four current models in a document-summarizing assistant with an email tool, finding that text-only attacks rarely worked but that one model (GLM 5.3 Flash) sent 58 of 60 attack emails without defenses. It recommends labeling untrusted content as data (cutting attack emails from 60 to 13 of 720), using a guardrail with a model allowlist and budget limit, checking every tool call with Armor (which blocked all 73 attempted attack emails at about 0.3 seconds added latency), and keeping secrets out of the prompt. Armor blocked real work in one case: a user approving a document's request without naming the address.
Why it matters: It offers a concrete, measured comparison of layered prompt-injection defenses, including where a tool-call guardrail blocks legitimate user requests.