datacron

Datacron

Local MCP server to query and maintain a Markdown vault from Claude, Codex, Gemini, or another stdio MCP client, without sending the whole vault into the context.

Français | English

Datacron indexes a folder of Markdown notes, exposes a local MCP server, then returns the relevant notes or chunks to the client instead of a full dump. The vault stays an ordinary Markdown folder: Datacron only adds a .datacron/ sidecar for the index, logs, internal ULIDs, history, and the operation journal.

What is in place

Surface	Current state
Vault reading	list_notes, get_note, resources datacron://vault/map, vault/info, policy/active
Search	SQLite FTS5/BM25, FR↔EN query expansion, temporal re-rank, ripgrep via search_regex
Local graph	Wikilinks and backlinks via get_backlinks
Writing	5 confined, reversible tools, disabled by default without DATACRON_WRITE_PATHS
Index	datacron index incremental, datacron reindex full, automatic repair on read
Evaluation	datacron eval over the real MCP pipeline: recall@k, MRR, nDCG, freshness, latency, and payload tokens
Guided setup	datacron setup: init + index + MCP registration in one command
Clients	Auto-detect and register via datacron setup --client all: Claude Desktop, Claude Code, Cursor, Gemini CLI, Antigravity, LM Studio, Codex CLI, Windsurf, VS Code
Memory protocol	Universal MCP instructions plus native global rules installed for supported clients
Distribution	Windows installer (Datacron-Setup.exe), standalone executable (PyInstaller) with no Python required, or installation from source

Local measurement of the tool/impl pipeline actually received by the agent, 19 questions, 8k-token / 20-result configuration, July 17, 2026:

recall@5       0.89
recall@10      0.95
recall@20      0.95
MRR            0.73
nDCG@10        0.79
latency p50    57 ms
latency p95    276 ms
payload tokens 90567

The tool now matches the raw store at recall@5 (0.89): the previous gap came from globally comparing scores produced by separate AND and OR queries, not from the response budget or a BM25 limitation. Repair-on-read throttling brings its own p50 down to 0.009 ms; the first full sweep of the session remains visible in p95. The golden set does not yet contain a forbidden_paths case and the vault has no indexed supersedes relationship.

Installation

Windows: one double-click installer

The easiest way on Windows: download Datacron-Setup.exe from the latest Release, double-click it, and pick your vault. No Python, no terminal, no administrator rights; Datacron registers itself with your AI clients automatically. Full guide: Windows installation.

From source

From a clone of the repository:

python -m pip install -e ".[dev]"

Or, to install only the application:

python -m pip install -e .

Runtime prerequisites:

• Python 3.11+
• ripgrep available on the PATH for search_regex
• a folder of Markdown notes
• a supported stdio MCP client, such as Claude Desktop, Codex CLI, or Gemini CLI

Quick start

The easy path - one command detects your AI clients, initializes the vault, indexes it, and registers Datacron everywhere:

datacron setup            # interactive; add --yes for all defaults

See the installation guide for options (--client, --scope, writing, durability). Or step by step:

datacron init /path/to/vault
datacron index --vault /path/to/vault
datacron status --vault /path/to/vault
datacron mcp install --client claude-desktop --vault /path/to/vault

The mcp install subcommand above is dedicated to Claude Desktop. For Codex CLI, Gemini CLI, Antigravity, LM Studio, Cursor, and the other clients, use multi-client setup with datacron setup --client <identifier> or auto-detection with --client all.

Add to LM Studio

LM Studio 0.3.17+ has one user configuration and no project scope. The preferred command is:

datacron setup --yes --vault "VAULT_PATH" --client lmstudio --scope user

For a Python installation where datacron-mcp is on PATH, the equivalent read-only configuration can also be imported with this official deeplink:

Add to LM Studio

The link imports this example. Open LM Studio's MCP editor and replace both <YOUR_VAULT> placeholders before starting the server:

{
  "mcpServers": {
    "datacron": {
      "command": "datacron-mcp",
      "args": [],
      "env": {
        "DATACRON_VAULT_ROOT": "<YOUR_VAULT>",
        "DATACRON_READ_PATHS": "<YOUR_VAULT>",
        "DATACRON_DURABILITY": "best-effort"
      }
    }
  }
}

The example does not enable write tools. CLI setup is safer for packaged installations because it writes the actual executable path automatically.

Restart the configured client or clients after installation.

To run the server manually:

datacron mcp serve --vault /path/to/vault

The direct script entry used by the installer is also available:

datacron-mcp

datacron-mcp reads the vault from DATACRON_VAULT_ROOT.

Configuration

datacron init creates .datacron/VAULT.yaml. That file can carry vault-local configuration, notably query expansion:

query_expansion:
  supervision: [monitoring]
  sauvegarde: [backup]
  restauration: [restore]
  chiffrement: [encryption]
  sécurité: [security]
  validité: [validity]
  certificat: [certificate]

Useful environment variables:

Variable	Default	Role
DATACRON_VAULT_ROOT	current directory or --vault	vault served by the server
DATACRON_READ_PATHS	empty	read allowlist; client setup sets it to the vault
DATACRON_WRITE_PATHS	empty	write allowlist; empty = write tools disabled
DATACRON_MAX_RESULT_COUNT	20	maximum number of results returned
DATACRON_MAX_RESULT_TOKENS	8000	token budget for search results
DATACRON_REPAIR_MIN_INTERVAL_SECONDS	30	minimum interval between repair-on-read sweeps; 0 = every read
DATACRON_GET_NOTE_MAX_TOKENS	25000	budget for get_note(format="full")
DATACRON_CHUNK_MAX_TOKENS	1024	target maximum chunk size
DATACRON_RIPGREP_PATH	rg	ripgrep binary

Path lists use the OS separator (: on Unix, ; on Windows).

Writing

Writes are deliberately OFF by default. Without DATACRON_WRITE_PATHS, write tools return a clear error and create no file.

To enable writing to a specific subfolder:

$env:DATACRON_VAULT_ROOT = "G:\_DATA"
$env:DATACRON_READ_PATHS = "G:\_DATA"
$env:DATACRON_WRITE_PATHS = "G:\_DATA\_memory"
datacron mcp serve --vault G:\_DATA

datacron setup can also apply the allowlist machine-wide (user environment variable, opt-in) so every MCP client inherits it; default: _memory, _drafts, _journal. See the setup guide.

Available write tools:

• create_note_ai: creates a typed Markdown note, without overwrite.
• append_journal: adds an entry under a heading of an existing note.
• set_frontmatter: updates lifecycle fields and the rejected options list without modifying the Markdown body.
• patch_note_section: replaces the content under an existing heading with CAS control.
• revert_note: restores the exact bytes of a version kept in history.

Guarantees:

• strict confinement within DATACRON_WRITE_PATHS
• atomic overwrite via temporary file + os.replace
• content-addressed history before modifying an existing note
• reconcile() after write to make the note immediately searchable
• local audit log

Concurrent multi-machine mode is not supported for writes: keep a single-writer rule on the vault.

MCP Tools

Reading

Tool	Description
list_notes	returns a paginated list, filterable by folder, tags, and frontmatter key/value pairs, with ULID, title, tags, aliases, and dates
get_note	reads a note by ULID, chunk id, or relative path, as paginated content, chunk, or heading outline
search_text	runs a BM25 search on the FTS5 index with ranked snippets and stale notes demoted by default
search_regex	runs a regex search via ripgrep and resolves the found lines to indexed chunks
get_backlinks	returns chunks whose wikilinks target a ULID or a resolved alias

Writing

Tool	Description
create_note_ai	creates a new typed _memory note, confined to allowed paths, without overwrite and with a durable journal
append_journal	adds a Markdown entry under a heading, with confinement, exact history, and atomic write
set_frontmatter	updates only the lifecycle fields, the rejected list, and the updated date, preserving the Markdown body
patch_note_section	replaces the content of an existing heading with CAS, exact history, and preservation of other sections
revert_note	restores a note from its content-addressed history; the operation stays durable, reversible, and audited

Operational

Tool	Description
get_health	returns the real state of index freshness, integrity, checksum, durability, and invariants
get_note_history	lists the committed operation metadata of a note without reading historical content or modifying the journal
audit_query	queries operation metadata by period, tool, or note without modifying the journal or the vault

Advisory (experimental)

Tool	Description
contradiction_scan	live, deterministic, bounded scan of contradictions/refinements between sections; proposes and confirms an explicit CAS call read-only, without ever writing automatically

MCP resources:

• datacron://vault/map
• datacron://vault/info
• datacron://policy/active

Search

search_text combines several signals:

• FTS5/BM25 for the base lexical score
• FR↔EN query expansion configured in VAULT.yaml
• conservative temporal re-rank:
  • a note referenced in another note's supersedes is strongly demoted
  • confidence: low and confidence: needs_verification apply a light penalty
  • include_superseded=true brings historical notes back up

search_regex stays literal: it applies neither query expansion nor temporal re-rank.

Privacy and security

• Datacron does no telemetry.
• Datacron calls no cloud LLM.
• The MCP client, for example Claude, Codex, or Gemini, may send the chunks that Datacron returns to its provider. Datacron does not send it the full vault.
• Content returned to clients is wrapped in <vault_content>...</vault_content>.
• Results are bounded by count and by token budget.
• Filesystem access is confined by DATACRON_READ_PATHS and DATACRON_WRITE_PATHS.
• MCP operations are audited in the local logs.

CLI commands

datacron setup                      # guided path: init + index + client config
datacron setup --yes                # all defaults, no prompts
datacron setup --client all --scope both --vault /path/to/vault
datacron setup --protocol           # also install client memory rules
datacron protocol install --client all
datacron init /path/to/vault
datacron status --vault /path/to/vault
datacron index --vault /path/to/vault
datacron reindex --vault /path/to/vault
datacron scrub-init --vault /path/to/vault
datacron scrub --vault /path/to/vault
datacron eval --questions examples/eval-questions.example.yaml --vault /path/to/vault
datacron eval --questions local/golden.yaml --vault /path/to/vault --save-baseline
datacron eval --questions local/golden.yaml --vault /path/to/vault --compare --json
datacron mcp serve --vault /path/to/vault
datacron mcp install --client claude-desktop --vault /path/to/vault  # Claude Desktop only
datacron unregister --client all --scope both --vault /path/to/vault
datacron protocol uninstall --client all

Current limitations

• No vector search / embeddings: the spike is ruled out on the current golden because tool-level recall@5 at 0.89 matches the BM25 store. Re-evaluate if an expanded golden falls below 0.85 with the same evaluation.
• No autonomous agent: the MCP client orchestrates.
• No GUI.
• No concurrent multi-machine writes.
• Client detection in datacron setup is best-effort (a config directory or a binary on the PATH); an install in a non-standard location may be missed and can then be configured by hand.

Documentation

Full index: docs/en/index.md | Index français.

To get started:

• Installation and configuration guide
• Frequently asked questions
• User guide

Technical references:

• Vault conventions (SPEC)
• Architecture and public surface
• Security boundary
• Integrity scrubber
• Operational health and durability
• Freshness contract

Development

python -m pip install -e ".[dev]"
ruff check .
ruff format --check .
mypy
pytest

License

Copyright 2026 Julien Bombled.

Licensed under the Apache License, Version 2.0.