A certificate of analysis (CoA) is a batch-specific document from a manufacturer or testing lab listing what was tested and the results — typically identity, purity or potency, and contaminants such as endotoxin or heavy metals — against defined specifications. In legitimate pharmaceutical supply chains, a compounding pharmacy receives a CoA with each lot of active pharmaceutical ingredient it buys and keeps it on file.
A CoA is only as trustworthy as the lab that produced it and the chain of custody behind it. Grey-market "research peptide" sellers routinely post CoAs, but independent test purchases have found the vial contents don't match the paperwork — so a CoA on a website is marketing until an accredited third party has verified it. See research peptides and GLP-1 medications.