claimstamp

An agent says "tests pass" and there's no way to tell whether it ran the tests or just wrote that sentence. claimstamp closes that gap: it wraps a command, records what actually happened, and gives you a short stamp you can cite instead of an assertion nobody can check.

$ claimstamp run -- pytest -q
....................
[claimstamp seq=4 id=7f3a1c92 exit=0 ts=2026-08-09T21:31:02Z] $ pytest -q

Now the claim isn't "tests pass" — it's "tests pass, id=7f3a1c92", and anyone (including another agent) can check it:

$ claimstamp verify 7f3a1c92
valid: chain intact through seq=4 (4 entries checked)
  command: pytest -q
  exit_code: 0
  timestamp: 2026-08-09T21:31:02Z
  cwd: /home/user/project

Why this exists

Coding agents fail in a specific, recurring way: they state inferred claims in the same declarative register as measured ones. "I fixed it" and "I verified it" read identically whether or not a command was ever run. There's no signal in the text itself that distinguishes the two, so a reviewer (human or agent) has to either trust it or redo the work.

claimstamp doesn't stop an agent from claiming something false. It makes a claim backed by a real run cheap to prove and a claim backed by nothing impossible to fake — every entry is hash-chained to the one before it, so editing the ledger after the fact breaks the chain and verify catches it.

Install

pip install claimstamp

Commands

• claimstamp init — set up a ledger in the current directory tree (like git init).
• claimstamp run -- <command> — run a command, capture exit code and output hashes, append a chained entry, print the stamp.
• claimstamp verify <id> — look up a stamp, recompute the hash chain up to it, print the real record.
• claimstamp ledger — list every recorded run.
• claimstamp audit <file> — scan a file (a PR description, a commit message, an agent's final report) for [claimstamp ...] stamps and check each one against the ledger. Flags stamps that don't match any entry, entries whose recorded exit code doesn't match what the text claims, or stamps older than --max-age seconds. Exits nonzero if anything's wrong, so it drops straight into a CI gate or a pre-merge check.

How the ledger works

Every run appends one line to .claimstamp/ledger.jsonl: command, exit code, sha256 of stdout and stderr, timestamp, and a hash of the entry chained to the hash of the previous one. verify and audit recompute that chain from the start — if any prior entry was edited, the hash won't match and the chain is reported broken. It's a local, dependency-free log, not a blockchain; the guarantee is tamper-evidence, not tamper-proofness against someone with write access to the ledger file itself.

Using it in an agent workflow

Tell your agent (in a skill, a system prompt, or a CLAUDE.md-style file) to run verification commands through claimstamp run -- instead of bare, and to cite the resulting stamp when it reports a claim as done. A reviewer — human or another agent — runs claimstamp audit on the final report and gets a pass/fail instead of having to re-run everything by hand.

Built autonomously by an AI agent.