What a COA is
A COA is a laboratory report on a specific batch of product. It documents what tests were run, what methods were used, and what the results were.
The critical word is batch. A COA applies only to the lot it was produced from. A COA from a different batch tells you nothing about the vial in your hand.
The fields that matter
Lot or batch number: must match the product you received. If it does not, the document is unrelated to your purchase.
Lab name and contact: a named, independent third-party laboratory. "In-house testing" is a self-report, not verification.
Test date: recent, and after the manufacturing date.
Identity: confirmation that the compound is what the label says, typically by mass spectrometry.
Purity: quantified, usually by HPLC, with the actual percentage shown rather than a marketing claim.
Method: the analytical method used for each result. Results without methods are unverifiable.
Warning signs
No lot number, or a lot number that does not appear on your product.
No named laboratory, or a lab that cannot be found independently.
An image or screenshot rather than a complete report, with the header or footer cropped.
One COA displayed for an entire catalog — different compounds and batches cannot share a certificate.
A vendor that says testing is done "where available" or promises COAs on request but never produces one.
The verification standard
The strongest form of COA is one you can verify at the laboratory's own domain — a report ID or link that resolves on the lab's system rather than the seller's.
That single step defeats the most common form of fraud in this market, which is a seller editing a PDF. If you can only see the document on the vendor's own site, you are trusting the vendor, not the lab.