Information Erasure Observatory
What the record lost, sealed so it cannot be lost again
Most censorship trackers answer one question: is this reachable right now? Palimpsest answers a different one. It measures what was removed or rewritten, across three layers of the record, and hash-chains every reading at the moment of capture so our own account of the erasure cannot be quietly edited afterwards. We observe from outside the wall and put no one inside it at risk.
An access index measures
Whether a site, an app or a tool is reachable at this instant. That is a real and useful measurement, and it is a snapshot. It cannot tell you that a page got shorter, that an encyclopedia entry moved to the state line, or that a model stopped giving an answer it used to give.
This observatory measures
What existed and is now gone or altered. Anyone can publish a live number, so the number alone proves nothing. The hard part is proving you did not edit your own history after the fact, and that is what the ledger below is for.
The composite reading
Figures on this page are read from erasure-observatory-latest.json when the page loads. Nothing here is typed in by hand. If the numbers below do not appear, the fetch failed or JavaScript is off, and the raw file and the ledger are served directly.
Composite Erasure Index
Every sealed reading, drawn
Erasure Index, full recorded history
erasure-observatory-history.jsonlEvery sealed composite reading is published in the raw history file, and this chart draws from it when the page loads.
Each point is one sealed ledger entry; the chain check on this page covers every one of them. A gap in the line is a run that did not commit, never an interpolation.
Network layer
Drawn from the same history file when the page loads.
Model layer
Drawn from the same history file when the page loads.
Narrative layer
Drawn from the same history file when the page loads.
The three layers
The composite is the mean of the layers that reported. A layer that is not reporting is shown as absent, with its reason, and is never folded in as a zero. A zero would say the record lost nothing on that layer, which is a different claim from having no measurement at all.
Independent cross checks
Separate instruments, measured by other people, pointed at the same thing. They do not feed the composite. They exist so that a layer moving on its own can be told apart from the world moving.
How this differs from an access index
The claim
Proving the measurement was not edited is the product
An observatory of erasure that can quietly revise its own past readings is not evidence of anything. It is a blog with charts. The ledger is what turns a number into something a sceptical reader can hold us to.
| An access observatory measures | whether a site, app or tool is reachable at this instant. |
| The Erasure Observatory measures | what existed and is now gone or altered: a page that got shorter, an encyclopedia entry rewritten to the state line, an answer a model used to give and now refuses. |
| Anyone can publish a live number | so the number alone proves nothing. The hard part is proving you did not edit your own history after the fact. |
| Our answer | every reading is sealed into a public, append-only, tamper-evident ledger at capture time. Recompute the chain yourself. A single altered or dropped past reading fails to verify. |
As the feed puts it
The ledger, and how to check it
Evidence
These are the values you recompute
The head hash covers every entry before it, and the merkle root is a single fingerprint of the whole ledger. Take them from this page, take the ledger file, and check that they agree without asking us anything. The registry roots are additionally deposited outside this project, which is what stops a wholesale rewrite. Where the roots are anchored.
Ledger state, as served
$ python3 scripts/verify_ledger.py
Sealed in the latest run
Method
Vantage-insensitive. Each layer ingests already-public data: OONI's aggregated measurements, the open encyclopedic record, and a panel of state-aligned models queried from outside the wall. No person inside China is ever asked to act. Judgement is lexical and auditable from the text. The composite is the mean of the layers that reported, and absent layers are shown as absent rather than zero-filled. Grounded in the trusted-public-archive literature (ARCHANGEL, arXiv:1804.08342) and the LLM-censorship measurement work (arXiv:2505.17441, arXiv:2506.12349). Not affiliated with OONI or Censored Planet. We ingest their open data with thanks.