evledger

A git-backed, append-only, machine-partitioned CloudEvents 1.0 event ledger (JSONL). Pure-stdlib core; optional CLI, MCP server, and a zero-build web visualizer.

• Append-only, never compress — events are immutable; the ledger is built for long-lived storage and replay.
• Machine-partitioned — events live at <root>/<machine>/<YYYY-MM>.jsonl, with a monotonic per-machine seq assigned at append under a file lock.
• CloudEvents 1.0 envelope — every record is a valid CloudEvent (specversion/id/source/type/time + machine/seq); the data attribute is an open channel for arbitrary JSON.
• Optional per-type schemas — register a data schema and validation is advisory (a slightly-off payload is still logged, never dropped).
• Stdlib-only core — the library and the visualizer have zero runtime dependencies. The CLI adds click; the MCP server adds the mcp SDK; both are optional extras.

Install

pip install evledger                # core library (stdlib only) + the `evledger` CLI*
pip install "evledger[mcp]"         # + the MCP server (`evledger-mcp`)
pip install "evledger[dev]"         # + pytest / ruff / mypy for development

* the evledger console script needs click; pip install "evledger[cli]" pulls it explicitly (it's also included by [dev]).

Library

The core is pure functions over an immutable event stream — easy to test, no hidden I/O beyond the store.

from evledger import LedgerStore, Query, new_event, query_events
from evledger.stats import counts_by_type, pair_events

store = LedgerStore(root="./ledger")

# Append — `seq` is assigned per-machine, monotonic, under a lock.
store.append(new_event(
    source="/laptop/app", type="com.example.job.start",
    machine="laptop", time="2026-05-30T10:00:00Z", data={"job": "sync"},
))

events = store.read_all().events                       # ordered by (time, seq)
starts = query_events(events, Query(type="com.example.job.*"))   # glob match
counts = counts_by_type(events)                        # {type: n}
durations = pair_events(events).durations              # pair *.start with *.end

See examples/quickstart.py for a runnable end-to-end walkthrough (python examples/quickstart.py).

Layers

CLI

The evledger command exposes the ledger over a small group:

evledger log --source /laptop/app --type com.example.job.start \
  --machine laptop --data '{"job":"sync"}'

evledger show --type 'com.example.*' --since 2026-05-01 --limit 50
evledger stats --by type --pair          # counts + paired *.start/*.end durations
evledger digest --since 2026-05-01        # deterministic rollup + anomaly flags
evledger serve                            # read-only web visualizer (localhost)

The ledger root resolves via --ledger-root → $CLAUDE_LEDGER_ROOT → <cwd>/ledger.

MCP server

The same log / query / stats operations are exposed to any MCP client (Claude Desktop, other agents) over stdio. The MCP SDK is imported lazily, so the core and CLI stay dependency-free.

# zero-install via uvx:
uvx --from "evledger[mcp]" evledger-mcp --ledger-root ~/.local/share/evledger

# or installed:
pipx install "evledger[mcp]"
evledger-mcp --ledger-root ~/.local/share/evledger

The ledger root is server-side configuration (captured at launch via --ledger-root → $CLAUDE_LEDGER_ROOT → <cwd>/ledger), not a tool argument.

Web visualizer

evledger serve starts a read-only, zero-build single-page app (stdlib http.server, no framework) bound to localhost: a filter panel, a wheel-zoom / drag-pan canvas timeline laned by source or type, a zoomable flame graph of derived *.start/*.end spans, and a sortable event table. JSON APIs (/api/events, /api/spans, /api/meta) back it. It never writes the ledger.

Storage layout

<root>/
  <machine-a>/
    2026-05.jsonl     # one CloudEvent per line, append-only
    2026-06.jsonl
  <machine-b>/
    2026-05.jsonl

Each line is a complete CloudEvent. Files are never rewritten or compressed — roll-up/aggregation happens at read time, so the raw record is preserved for the life of the ledger.

Development

pip install -e ".[dev,mcp]"
ruff check .
mypy evledger
pytest -q

CI (GitHub Actions) runs ruff + mypy + pytest across Python 3.10–3.13.

License

MIT — see LICENSE.