Each Fonteum snapshot is SHA-256 digested, Ed25519 signed, and hash-chained to the one before it — a Certificate-Transparency-style log where any change to a published fact is detectable by a single recomputation.
f55bb4f38924fc319fcbdac42a1d95ad7c0edd9f0c4d32eb5697bbe9136033a0Every dataset refresh produces a complete snapshot, SHA-256 digested at write time so its content is fixed to a single fingerprint.
The digest is signed with Fonteum's Ed25519 key. The matching public key is published, so anyone can confirm the signature offline.
Each digest references the prior snapshot's hash, forming an append-only, tamper-evident chain — alter one row and every later hash stops matching.
Diff two snapshots of a dataset and get every changed field with its full 14-tuple provenance attached. Try it now with the public pk_dx_sample key:
curl -s https://fonteum.com/api/v1/snapshots/diff \
-H "Authorization: Bearer pk_dx_sample" \
-H "Content-Type: application/json" \
-d '{
"dataset": "nppes",
"from_snapshot": "2026-04-01T00:00:00Z",
"to_snapshot": "2026-05-01T00:00:00Z",
"fields": ["taxonomy", "addresses"]
}'Response shape
{
"dataset": "nppes",
"from_snapshot": { "digest": "…", "signature": "…", "signing_key_fingerprint": "…" },
"to_snapshot": { "digest": "…", "signature": "…", "signing_key_fingerprint": "…" },
"changes": [
{
"npi": "1234567890",
"field": "taxonomy",
"change_type": "modified",
"before": { "value": "…", "provenance": { /* 14-tuple */ } },
"after": { "value": "…", "provenance": { /* 14-tuple */ } }
}
],
"summary": { "total_changes": 2, "added": 0, "removed": 0, "modified": 2 }
}Full reference: /docs/api/snapshots-diff
5ea9547e26ebaf18425098106658d4f979c6380c90ea7d0ea9f11bf917e71c87Call the snapshot diff API with pk_dx_sample, or drop our MCP server into your agent. No signup. No credit card. Live demo key.