Methodology

01 · Where the data comes from

Pricing. Prices are collected by automated scrapers that read each vendor's public storefront once a week (currently Mondays, ~06:00 UTC). For every product size a vendor lists, we record:

• peptide and size (e.g. BPC-157, 5mg)
• listed price
• price per mg — normalized across sizes and kit formats so vendors compare on equal terms
• in-stock status
• the product page URL it came from
• the timestamp it was collected

Vendors that block automated collection are either left out or updated by hand; manually entered rows are labeled and reviewed quarterly.

Purity. Purity figures come from Finnrick Analytics — an independent testing program that sends vendor samples to third-party laboratories (including Janoshik) for HPLC analysis and publishes the results. Where we show a purity number, it carries a link to the underlying Finnrick page so you can check the source, the sample count, and the test dates yourself; rows tested at Janoshik are labeled accordingly. Where vendors publish their own certificates of analysis, we link the COA from the product row — a vendor-published COA is a claim, not an independent result. When no third-party test exists for a product, we may show the vendor's own claimed purity — always labeled as such, never blended with independent results. “No data” means no published third-party tests. It is not a failed result.

A necessary caveat about lab results. Most public test records — Janoshik’s included — come from vendor-submitted samples: the vendor picks which vial gets tested and sends it in. A passing result proves that vial, not the batch you’ll receive, and vendors that test at all are self-selecting. We show these results because a documented test is still better than none — but read a pass as “at least one good vial exists,” not “every vial is good.”

COA verification. Where vendors publish their own certificates of analysis, we don’t take them at face value: each document is cross-checked against the Janoshik public test record. A badge on vendor and peptide pages says exactly what was checked — Verified vs public record only when the document’s own lab task number resolves to a real public test attributed to that vendor (document identity confirmed, and any claimed purity matches within its own rounding); consistent with public record when the vendor, compound, and purity agree with a record but the document’s identity can’t be proven — a similarity match is never called verified; vendor-published only when no public record exists to check; needs review when the evidence is ambiguous — a task number absent from the record, a record filed by a different submitter (borrowed and shared-supplier COAs exist, so that alone is not an accusation), or a record too incomplete to confirm or deny the claim; and mismatch only when the document affirmatively contradicts the record — wrong figures or a different compound entirely. Edited COAs are common enough in this market that we consider the check worth building.

Vendor information. Vendor names, URLs, and listings come from the vendors' public sites and community research. Presence on this site is not an endorsement.

02 · How the data is validated

Scraped data is wrong sometimes. We run a validation pass over the live dataset that checks four things:

• Freshness. Every price row carries its collection timestamp. Data under 7 days old is fresh; 7–30 days is stale; over 30 days is treated as unreliable and flagged for review. Timestamps are shown wherever prices appear — if data is old, you'll see it.
• Outliers. Any price-per-mg more than 2.5× above or 0.4× below the peer median for the same peptide and size is automatically flagged. Flagged rows are reviewed before they're trusted — extreme outliers are usually scraper errors, but we don't delete them silently.
• Scrape health. Every scraper run is logged with how many records it produced. A run that saves zero records counts as a failure, not a success. Per-vendor success rates and failure streaks are tracked; vendors with sustained failures are labeled stale rather than shown as current.
• Offer integrity. Prices must be positive, sizes must parse to a positive weight, per-mg must equal price ÷ size, and source links must be well-formed. Freshness labels are recomputed from each row's timestamp — a stale row can never show up as fresh.

03 · How rankings work

Vendor order on the comparison table is computed entirely from the data:

• Default sort — “Best $/mg”: lowest normalized price per milligram across the vendor's in-stock size tiers. Only when nothing is in stock does a listed (unavailable) price set the headline — and the stock column says so.
• Purity sort: highest third-party (Finnrick) average purity for the selected peptide; vendor-claimed purity is used only when no independent result exists.

That is the whole formula. There is no manual adjustment, no hidden weighting, and no input a vendor can pay to change.

05 · Corrections

We get things wrong — scrapers misread kit sizes, vendors relabel products, lab results update. If you spot an error (a price, a size, a missing vendor, a wrong grade), email hello@pepvendors.com with the page and what's off. Confirmed errors are corrected, and material fixes are noted publicly. Vendors can dispute their own data through the same channel.

06 · Scope and legal

• All compounds listed are sold by third-party vendors for laboratory research use only — not for human consumption. Nothing on this site is medical advice.
• We do not verify the quality, safety, or legality of any vendor or product. Inclusion means we collected data about them — nothing more.
• Prices and stock can change between weekly scrapes; always confirm on the vendor's site before ordering.
• You are responsible for compliance with the laws in your jurisdiction before purchasing or using any research compound.

07 · Questions