1. Identify the exact item
We match what you type against model numbers and names in the Tethered Trust graph. Exact model numbers matter: different suffixes can be different products. If we can't identify something, we say so and tell you what to look up.
2. Apply fixed rules
Most compatibility comes down to a few physical and electrical facts. We check them with deterministic rules, not guesses:
- Computers: memory generation and module size, soldered vs upgradeable, M.2 length, key and NVMe/SATA, PCIe generation, USB-C Power Delivery wattage.
- Standards and platforms: lens mounts and adapters, cordless battery platforms, ink and toner cartridge families (including region locks), wireless charging (Qi, Qi2, MagSafe), watch band sizes, smart-home protocols (Matter, Thread, Zigbee) and bulb bases. A product "takes" some standards and "fits" others; we compare them and include the known exceptions.
- Explicit part listings: when a manufacturer lists a specific part for a specific model (an OEM water filter, say), that listing wins.
- Installation fit: product dimensions plus typical clearances and the connections a location has.
3. What "verified" means
A product or listing is verified when a person has checked it against the manufacturer's own page or an authoritative spec database (for example Lenovo PSREF or Apple Tech Specs). Each one shows its source link and the date it was checked. Anything else is labeled awaiting review, and answers that rely on it say verified: false.
When nobody has added a product yet, an AI model may read its published specs so we can still give an answer. Those readings are clearly marked, lower the confidence, and are held for human review before they're used for anyone else.
4. What the confidence number means
| Where the specs came from | Starting confidence |
|---|---|
| Verified graph records | 97% |
| Specs you typed (e.g. "16GB DDR4-3200 SODIMM") | 88% |
| Graph records awaiting review | 75% |
| Read by AI from published specs | 70% |
The answer uses the weakest of the two items. "Compatible with notes" takes a small deduction; "can't confirm" is capped at 60% and "need more detail" at 30%. Clear physical mismatches (wrong memory generation, a drive that's too long) get a small boost, and three or more "it fit" reports from buyers with none failing add a little more.
5. How long an answer stays good
Every answer carries a valid_until date based on its weakest source: up to a year after a verified record was last checked, 30 days for records awaiting review or specs you typed, 7 days for AI readings, 90 days for installation-fit checks and one day when we still need detail. After that, check again.
6. Signed receipts
Each compatibility and fit answer comes with a signed receipt: the verdict, the products as we identified them, the evidence and its dates, signed with an Ed25519 key (a standard JWS). Our public keys are at /.well-known/tethered-trust-keys.json, and anyone can check a receipt with POST /v1/receipts/verify or the verify_receipt tool.
What a receipt proves, and what it doesn't. A valid receipt proves that Tethered Trust issued that verdict at that time and that nobody has changed it since. It does not prove the verdict is correct. If the records behind it change later, checking the receipt says so ("data changed").
7. Buyers make it better
After a purchase, people and AI agents can report whether it fit. Reports are kept at four levels: self-reported (website), agent-reported (anonymous API or MCP), partner-reported (accountable API key holders) and order-confirmed (we've seen order evidence). All of them show up as evidence; only the last two can raise confidence. A "didn't fit" report sends the answer to our review queue. You can also report a wrong answer directly.
8. Independence
Verdicts are never for sale. If we ever earn money from retailers or manufacturers (for example affiliate links or paid verification of a catalog), we'll say so on the page, and it won't change what the rules say fits.
9. Limits
We can be wrong: manufacturers change parts mid-model, regions differ and firmware changes behavior. Answers are informational. Always confirm with the manufacturer before you buy or install, especially for anything electrical, gas or water related. See the Terms.