provtrail

Source provenance ledger for LLM-assisted research.

provtrail is an append-only, hash-chained JSONL ledger for recording which sources were captured during LLM-assisted research, and when. It has no runtime dependencies beyond the Python standard library. It includes a command-line interface, a Claude Code Stop hook, an agent skill, and an optional MCP server. What a verified ledger does and does not prove is set out under "What the ledger establishes, and what it does not".

Installation

pip install provtrail            # from PyPI
pip install "provtrail[mcp]"     # with the optional MCP server dependency
pip install -e .                 # from a clone

The core package and the Stop hook require Python 3.9 or later. The [mcp] extra requires Python 3.10 or later, because the mcp package does not support 3.9.

Usage

# append a record
provtrail add ./ledger.jsonl --url "https://example.com/report" \
  --title "Example report" --claim "X happened in 2024"

# append a record identified by content rather than URL
provtrail add ./ledger.jsonl --content-file ./report.pdf --kind file --path report.pdf

# verify the chain (add --check-files to re-hash referenced files)
provtrail verify ./ledger.jsonl

# report whether a valid record exists in a time window and/or for a session
provtrail check ./ledger.jsonl --since 2024-01-01T00:00:00Z
provtrail check ./ledger.jsonl --since 2024-01-01T00:00:00Z --until 2024-01-02T00:00:00Z
provtrail check ./ledger.jsonl --session-id abc123

# print the last record's seq:record_hash
provtrail head ./ledger.jsonl

# verify against one or more previously recorded anchors
provtrail verify ./ledger.jsonl --expect 42:sha256:<64-hex-digest>
provtrail verify ./ledger.jsonl --expect-file ./anchors.txt

Exit codes:

Command	0	1	2
add	record appended	contract violation, invalid kind, ledger fails verification, or lock timeout	usage error
verify	no violations	violations found (including a missing or mismatched --expect anchor)	malformed --expect/--expect-file entry
check	all states without --enforce	-	MISSING under --enforce; usage error
head	printed seq:record_hash	ledger has no records, or fails verification	usage error

check returns one of three states:

• PRESENT: the ledger verifies and contains a matching record.
• MISSING: the ledger verifies and contains no matching record.
• UNKNOWN: the check could not be performed (ledger absent, chain fails verification, or a timestamp argument is unparseable).

UNKNOWN never produces a non-zero exit, including under --enforce: a failed check is reported, not treated as a confirmed absence.

Anchoring

provtrail verify alone cannot tell a ledger that lost its last few records from one that never had them: a truncated file, or a whole file rewritten from a truncated copy, still verifies as a valid, shorter chain. Detecting that requires a record of the last record_hash kept somewhere the ledger itself cannot reach.

provtrail head LEDGER prints that anchor as seq:record_hash (--json for {"seq": N, "record_hash": "sha256:..."}); it exits 1 if the ledger has no records or fails verification. Store the anchor outside the ledger, for example in a signed git commit, a separate append-only log or a timestamping service, and check it later with provtrail verify --expect.

Anchoring in a signed git commit:

anchor=$(provtrail head ./ledger.jsonl)
git commit --allow-empty -S -m "provtrail anchor: $anchor"

The commit's GPG/SSH signature and its position in the git history then vouch for when that anchor was recorded; later, git show --show-signature <commit> recovers the anchor text to check with provtrail verify --expect. Anchoring with a timestamping service (RFC 3161) instead:

anchor=$(provtrail head ./ledger.jsonl)
echo -n "$anchor" > anchor.txt
openssl ts -query -data anchor.txt -no_nonce -sha256 -out anchor.tsq
curl -s -H "Content-Type: application/timestamp-query" --data-binary @anchor.tsq \
  https://freetsa.org/tsr > anchor.tsr

anchor.tsr is a timestamp token binding the anchor's hash to a time attested by the timestamping authority; keep it alongside anchor.txt. provtrail itself does not sign, timestamp or transmit anything; both examples are external to the ledger.

Checking stored anchors:

provtrail verify ./ledger.jsonl --expect 42:sha256:<64-hex-digest>
# or, for several anchors collected over time, one per line:
provtrail verify ./ledger.jsonl --expect-file ./anchors.txt

--expect-file lines are seq:sha256:<64 hex>; blank lines and lines starting with # are ignored. Each anchor must match a record with that exact seq and record_hash, checked against the recomputed hash (not merely the stored one), so a forged replacement record is still caught. Violations: ANCHOR_MISSING (no record at that seq, e.g. the ledger was truncated) and ANCHOR_MISMATCH (a record exists there, but its hash differs). A malformed --expect or --expect-file entry is a usage error (exit 2), not a violation.

Library equivalents: Ledger.head() returns (seq, record_hash) or None; Ledger.verify(..., expect=[(seq, record_hash), ...]) checks the same anchors and folds ANCHOR_MISSING/ ANCHOR_MISMATCH into its usual violation list.

What the ledger establishes, and what it does not

The ledger establishes:

• that each record is unchanged since it was appended, and that records have not been edited, reordered or removed in the middle of the file (provtrail verify recomputes every hash and walks the prev_hash chain);
• that, for a record with a content_hash, the referenced bytes are the ones that were hashed (verify --check-files re-hashes files stored under the ledger's directory).

The ledger does not establish:

• that a source was actually read or consulted. A record can be written without reading anything, and the tool cannot tell a genuine capture from a fabricated one;
• that a URL was reachable, or that supplied content came from that URL. provtrail never makes network requests;
• that a source supports the claim stored next to it;
• when a capture happened, beyond the caller's own clock. captured_at is written by the process that appends the record; it is not a trusted timestamp;
• that nothing was removed from the end of the file, or that the whole file was not rewritten, unless an anchor was recorded outside the ledger beforehand. provtrail head prints the last record's seq:record_hash; checking a stored anchor later with provtrail verify --expect detects truncation and whole-file rewrites (see "Anchoring"). Without a stored anchor, neither is detectable.

The Claude Code Stop hook checks that at least one valid record exists for the current session or turn. It does not know how many sources the session drew on, so one record satisfies it as fully as ten. Proving that every source was captured would require matching each tool event (each web fetch, each file read) to a ledger record, which provtrail does not do. The hook is a reminder to capture sources, not an audit control.

Record contract

provtrail verify accepts a record when all of the following hold (each failure has a code, listed under "Violation codes"):

• schema is provtrail/v1, and seq, prev_hash, record_hash and id are consistent with the chain;
• captured_at is an RFC 3339 date-time: T separator, optional fractional seconds, and Z or a ±HH:MM offset (a leap second :60 is accepted and treated as :59);
• source_url is a non-empty string, or content_hash is sha256: followed by 64 lower-case hex digits, or both;
• kind is one of url, search, scrape, file, manual (provtrail add defaults it to url);
• every key is a v1 field, and every field has its documented type.

tool, query, title, claim, snippet, archived_url, path, session_id and extra are optional. provtrail add applies the same field checks before writing, so it never appends a record that verify would reject.

Record schema (v1)

The JSON Schema (draft 2020-12) is in schema/provtrail-record.v1.json. It is a structural check of types, required fields and patterns. provtrail verify is the normative check: it parses captured_at with the ledger's own RFC 3339 rules, recomputes every hash and walks the chain, which a schema validator does not do.

Field	Type	Notes
schema	string	Always "provtrail/v1".
seq	integer	1-based, contiguous within a ledger.
id	string	"ev_" followed by the first 16 hex characters of the record_hash digest.
captured_at	string	RFC 3339 timestamp, set by the appending process. Required.
source_url	string	Required unless content_hash is set.
content_hash	string	sha256:<64 hex>. Required unless source_url is set.
kind	string	url, search, scrape, file, or manual. Default url.
tool	string	Capturing tool or backend, e.g. web-search:api.
query	string	Search query, if any.
title	string	Source title.
claim	string	The statement the source is recorded for. Not checked.
snippet	string	Short excerpt.
archived_url	string	URL of an archived copy.
path	string	Artifact path relative to the ledger's directory. Absolute paths and paths that leave the directory are rejected.
session_id	string	Identifier of the capturing session.
extra	object	Free-form metadata.
prev_hash	string or null	record_hash of the previous record; null for seq 1.
record_hash	string	sha256: digest of the canonical JSON of the record, excluding record_hash and id.

Canonical JSON is json.dumps(record, sort_keys=True, separators=(",", ":"), ensure_ascii=False, allow_nan=False) encoded as UTF-8. NaN and Infinity are rejected. extra may hold only JSON values: objects with string keys, arrays, strings, numbers, booleans and null. Anything JSON would rewrite or cannot represent, such as a None or integer key, a tuple, a set or bytes, is rejected. Subclasses of the built-in types (an OrderedDict, an IntEnum member) are accepted and read back as the plain type, with an equal value.

Violation codes

Code	Meaning
INVALID_JSON	Line is not valid UTF-8, not valid JSON, or not a JSON object.
WRONG_SCHEMA	schema is not provtrail/v1.
MISSING_CAPTURED_AT	captured_at is absent or empty.
INVALID_CAPTURED_AT	captured_at is present but not parseable.
MISSING_SOURCE_LOCATOR	Neither source_url nor a valid content_hash is present.
INVALID_KIND	kind is missing or not one of url, search, scrape, file, manual.
INVALID_CONTENT_HASH	content_hash is present but not a well-formed sha256:<64 lower-case hex> string.
UNKNOWN_FIELD	The record has a key that is not a field of the v1 schema.
INVALID_FIELD_TYPE	A field has the wrong type: seq not an integer >= 1, a string field holding a non-string, extra not an object or holding a non-JSON value, prev_hash neither null nor sha256:<64 lower-case hex>.
BAD_SEQ	seq does not follow the previous record.
CHAIN_BROKEN	prev_hash does not match the previous record's record_hash.
HASH_MISMATCH	record_hash does not match the recomputed value.
ID_MISMATCH	id does not match the value derived from the recomputed hash.
INVALID_PATH	path is absolute or leaves the ledger's directory (with --check-files, also after following symlinks).
FILE_MISSING	--check-files: referenced file is absent or unreadable.
FILE_HASH_MISMATCH	--check-files: file content does not match content_hash.
ANCHOR_MISSING	verify --expect/--expect-file: no record exists at the expected seq.
ANCHOR_MISMATCH	verify --expect/--expect-file: a record exists at that seq, but its hash differs.

Claude Code integration

Stop hook

The Stop hook runs at the end of every turn and reports, or optionally blocks, when the ledger has no valid record for the current session. It runs regardless of which tools the model called.

1. Add the Stop entry from integrations/claude-code/settings.example.json to the project's .claude/settings.json. It runs the provtrail-stop-hook command installed with the package; if that command is not on the PATH Claude Code uses, give its absolute path, or use python -m provtrail.stop_hook with the interpreter where provtrail is installed. From a source checkout, point the command at integrations/claude-code/stop_hook.py.
2. Create .provtrail.json in the project root:

   { "ledger": "./ledger.jsonl", "mode": "report" }
   

   Alternatively set PROVTRAIL_LEDGER and, optionally, PROVTRAIL_MODE.

Without a configured ledger the hook exits silently.

Modes:

Mode	MISSING	UNKNOWN
report (default)	systemMessage, never blocks	systemMessage, never blocks
enforce	blocks	systemMessage, never blocks
strict	blocks	blocks

PRESENT never blocks. A hook re-invocation (stop_hook_active true) never blocks either, which prevents Stop-hook loops. report is the recommended mode; see "What the ledger establishes" for why enforce and strict are not audit controls.

Scope of the check:

• If the hook payload includes session_id, only records with the same session_id count.
• Records dated more than 300 seconds after the hook runs do not count (a margin for clock differences between the writer and the hook).
• The window opens at the first timestamp found in the session transcript, when there is one (scope: "session", the default; see "Turn scope" below for scope: "turn"). This relies on the transcript's JSONL format, which Claude Code does not document; if the format changes, the hook falls back to session_id alone, or to UNKNOWN when neither is available.
• An absent ledger file in an existing directory counts as MISSING; an absent directory as UNKNOWN (probably a misconfigured path).
• Unexpected errors, such as a malformed .provtrail.json or an invalid mode or scope, are reported as a systemMessage; in strict mode they block, unless stop_hook_active is true. The hook always exits 0.

Configuration precedence (shared by the hook and the MCP server through provtrail.config.resolve_config and provtrail.config.resolve_scope):

• Ledger path: PROVTRAIL_LEDGER, then "ledger" in <project>/.provtrail.json. Relative paths resolve against the project directory.
• Mode, resolved independently of the ledger path: PROVTRAIL_MODE, then the legacy PROVTRAIL_ENFORCE=1, then "mode" in .provtrail.json, then the legacy "enforce": true, then report. An invalid mode value is an error, not a silent fallback.
• Scope, resolved the same way (minus the legacy aliases): PROVTRAIL_SCOPE, then "scope" in .provtrail.json, then session. An invalid scope value is likewise an error.

Turn scope

scope: "turn" narrows the check from "was something captured this session" to "was something captured during the turn that is ending". Instead of opening the window at the transcript's first timestamp, it opens at the LAST transcript entry that is a human prompt: type == "user", isMeta not true, isSidechain not true, and message.content either a plain string or a list containing no tool_result block. Two other kinds of transcript entry also have type == "user" and must not be mistaken for a prompt: Stop-hook feedback (isMeta: true, injected by a previous hook run) and tool-result entries. If no qualifying entry exists, or the transcript cannot be read, the state is UNKNOWN; turn scope never falls back to session scope's first-timestamp behaviour. The session_id filter and the 300-second future bound still apply on top of the turn window.

This transcript shape is observed, not documented by Claude Code, and may change without notice. It was measured in two Claude Code 2.1.269 claude -p transcripts: a human prompt is a plain string message.content with no isMeta; a tool result is a list message.content containing a tool_result block, plus a top-level toolUseResult field on the entry; Stop-hook feedback is a string message.content with isMeta: true.

Agent skill

integrations/claude-code/SKILL.md describes when and how the model should call provtrail add. Install it as a project or user skill.

MCP server

provtrail-mcp (module provtrail.mcp_server) is an MCP server over stdio that exposes provtrail_add and provtrail_verify. It requires the [mcp] extra and works with mcp 1.x and 2.x.

Neither tool takes a ledger path; the server resolves it from its working directory with the same configuration rules as the hook. provtrail_add accepts source_url, content, content_path, tool, kind, claim, title, query, snippet, archived_url and session_id. A content_path must resolve, after following symlinks, inside the ledger's directory; the file is hashed from its raw bytes and its relative path is stored in path. The server also passes the ledger's directory to Ledger.add as content_root (see below), so the library enforces the same rule a second time. session_id defaults to the CLAUDE_CODE_SESSION_ID environment variable, which Claude Code sets for Bash tool subprocesses and stdio MCP server processes.

Ledger.add(..., content_root=...)

When content_root is given together with content_path, the realpath of content_path must resolve inside content_root, else Ledger.add raises ValueError before writing anything. With the default None, any readable content_path is hashed. This is a path-containment check, not a security sandbox: it resolves content_path once, at check time, so it does not stop a file being replaced by a symlink pointing outside content_root between the check and the read (a time-of-check/time-of-use race), and it does not defend against hardlinks or other filesystem-level aliasing. Use it against accidental misuse (a caller-supplied path landing outside the intended directory), not as a defense against an adversarial filesystem.

Limitations

• Tamper-evident, not tamper-proof, without a stored anchor. Editing, reordering or removing a record in the middle of the ledger is always detected. Removing records from the end leaves a valid, shorter chain, and anyone who can rewrite the whole file can build a new consistent one; provtrail verify alone cannot tell that apart from a ledger that legitimately never had those records. Detecting it requires recording an anchor outside the ledger first and checking it later (see "Anchoring"); without a stored anchor, it is undetectable.
• A ledger that fails verification is not extended. add verifies the ledger before appending and refuses if any violation is found. Repair the file or start a new ledger.
• Cost of appending. Every add verifies the whole ledger, so appending is linear in the ledger's length. Measured on 2026-09-12 on a Windows 11 laptop (Intel Core i5-13420H, 32 GB RAM, NVMe SSD; Python 3.13.14; Ledger.add in a loop, timing the last 100 appends at each size): at 1,000 records, append latency p50 = 36.3 ms, p95 = 45.9 ms, and verify on the full ledger takes 0.04 s; at 10,000 records, append p50 = 176.8 ms, p95 = 205.5 ms, and verify takes 0.18 s. This is fine for research sessions of hundreds or thousands of records, not for very large ledgers.
• Advisory locking. <ledger>.lock serialises concurrent add calls on one machine. It does not stop a process that ignores it, is not reliable on network file systems, and a lock left by a crashed process must be removed by hand.
• Canonical JSON is Python's. The hash input is Python's json.dumps output as specified above, not RFC 8785 (JCS). A verifier in another language must reproduce it exactly; see tests/vectors/canonical_v1.json for worked input/output pairs covering ASCII, non-ASCII, nested objects, integers, a float, and prev_hash: null.
• The library API's containment is opt-in, not a sandbox. Ledger.add(content_path=...) hashes any file the caller can read unless content_root is passed (see above), and even then it is a containment check, not a defense against a hostile filesystem.
• Plain-text storage. The ledger is unencrypted JSONL. Do not store credentials, tokens or personal data in any field.

Development

python -m unittest discover -s tests -v

License

MIT. See LICENSE.