MDQL

A database where every entry is a markdown file and every change is a readable diff.

MDQL turns folders of markdown files into a schema-validated, queryable database. Frontmatter fields are metadata columns. H2 sections are content columns. The files are the database — there is nothing else. Every file reads like a normal markdown document, but you get full SQL: SELECT, INSERT, UPDATE, DELETE, JOINs across multiple tables, ORDER BY, and aggregation.

Your database lives in git. Every insert, update, and migration is a readable diff. Branching, merging, and rollback come free.

Quick start

cargo install mdql
mdql validate examples/strategies/
# All 100 files valid in table 'strategies'

mdql query examples/strategies/ \
  "SELECT title, composite FROM strategies ORDER BY composite DESC LIMIT 5"

title                                                                composite
-------------------------------------------------------------------  ---------
Bridge Inflow to Destination Chain → DEX Liquidity Pressure                500
DeFi Protocol TVL Step-Change → Governance Token Repricing Lag             500
Lending Protocol Daily Interest Accrual Liquidation Threshold Creep        500
USDC Circle Business-Day Redemption Queue — Weekend Premium Decay          490
Cascading Liquidation Chain — Second-Order Collateral Asset Short          480

Why MDQL

• Zero infrastructure. No server, no Docker, no connection strings. git clone and you have the database. rm -rf and it's gone.
• Data review via pull requests. Data changes go through the same PR review process as code. A reviewer reads the diff of an INSERT the way they read a code change.
• Branch-level isolation. An agent works on a feature branch, inserts and updates entries freely, and the main database is untouched until merge. Multiple agents work in parallel without coordination.
• No serialization boundary. The storage format is the readable format. An LLM sees a well-structured markdown document, not a JSON blob or SQL dump.
• Graceful degradation. If you stop using MDQL tomorrow, you still have a folder of valid markdown files. No proprietary format to export from.
• Section-level content columns. Long-form structured prose — a hypothesis, a methodology, kill criteria — is a first-class queryable column. SELECT Hypothesis FROM strategies WHERE status = 'LIVE'.
• Every unix tool still works. grep -r "funding" strategies/ works. wc -l strategies/*.md works. diff works.
• Self-documenting schemas. The schema file is a markdown document. Its body explains the fields, conventions, and rationale. An LLM reading _mdql.md gets both the machine-readable schema and the human context for why fields exist.
• Schema migrations are diffs. ALTER TABLE RENAME FIELD rewrites every file. The migration shows up as a git diff.
• Audit trail for free. git blame strategies/bad-debt-socialization-event-token-short.md tells you who changed what and when.

Directory structure

my-project/
  _mdql.md                    # type: database — config + foreign keys
  strategies/
    _mdql.md                  # type: schema — table schema + docs
    bad-debt-socialization-event-token-short.md
    aave-utilization-kink-rate-spike-borrow-unwind-short.md
    ...
  backtests/
    _mdql.md                  # type: schema
    bt-bad-debt-socialization-binance.md
    ...
  src/                        # no _mdql.md — invisible to MDQL
  docs/                       # no _mdql.md — invisible to MDQL

A _mdql.md file marks a directory as part of an MDQL database. The type field in frontmatter determines what it is — database at the root, schema in each table folder. Directories without _mdql.md are ignored, so MDQL coexists with any project structure.

How it works

One folder = one table. One markdown file = one row.

A row file looks like this:

---
title: "Bad Debt Socialization Event — Token Short"
status: HYPOTHESIS
mechanism: 7
categories:
  - defi-protocol
  - lending
created: "2026-04-03"
modified: "2026-04-05"
---

## Hypothesis

When an on-chain lending protocol accumulates bad debt that exceeds
its reserve buffer, the smart contract mints governance tokens...

## Structural Mechanism

The protocol's shortfall module triggers an auction...

• YAML frontmatter fields are metadata columns (title, status, mechanism, ...)
• H2 sections are content columns (Hypothesis, Structural Mechanism, ...)
• The path (filename) is the implicit primary key
• created and modified are reserved timestamp fields, auto-managed by mdql stamp
• All columns are queryable with SQL

_mdql.md files

Every MDQL-managed directory has a _mdql.md file. The type field in frontmatter says what kind.

Table schema (type: schema)

---
type: schema
table: strategies
primary_key: path

frontmatter:
  title:
    type: string
    required: true
  mechanism:
    type: int
    required: true
  categories:
    type: string[]
    required: true

h1:
  required: false

sections: {}

rules:
  reject_unknown_frontmatter: true
  reject_unknown_sections: false
  reject_duplicate_sections: true
---

# strategies

Documentation about this table goes here.

Supported types: string, int, float, bool, date, string[]

Database config (type: database)

---
type: database
name: zunid

foreign_keys:
  - from: backtests.strategy
    to: strategies.path
---

# zunid

Trading strategy research database.

The markdown body in both cases is documentation — ignored by the engine, useful for humans and LLMs.

Foreign key validation

Foreign keys defined in the database config are validated automatically. No setup required.

At load time: Every call to load_database() checks all FK constraints. If backtests.strategy references a file that does not exist in strategies.path, the error is returned alongside the data. CLI commands (query, validate, repl) print FK warnings to stderr.

In the REPL: A filesystem watcher runs in the background. If you rename or delete a file in another terminal, the REPL detects the change within 500ms and prints any new FK violations.

In the web UI: Same filesystem watcher runs as a background task. FK errors are available at GET /api/fk-errors.

With mdql validate: When pointed at a database directory (not just a single table), reports per-table schema validation summaries followed by FK violations:

mdql validate examples/

Table 'strategies': 100 files valid
Table 'backtests': 18 files valid
Foreign key violations:
  backtests/bt-broken.md: strategy = 'nonexistent.md' not found in strategies

NULL FK values are not violations — a backtest with no strategy set is valid.

Python API

pip install mdql

Database and Table

from mdql import Database, Table

db = Database("examples/")
strategies = db.table("strategies")

SELECT with JOINs

Database.query() runs SQL across all tables in the database, including multi-table JOINs.

rows, columns = db.query(
    "SELECT s.title, b.sharpe, b.status "
    "FROM strategies s "
    "JOIN backtests b ON b.strategy = s.path"
)
# rows: list of dicts, one per result row
# columns: list of column names

Single-table queries

Table.query() runs a SELECT query on one table and returns structured results.

rows, columns = strategies.query(
    "SELECT status, COUNT(*) AS cnt FROM strategies GROUP BY status"
)
# rows: list of dicts
# columns: list of column names

Load rows with filtering

Table.load() returns all rows, optionally filtered by a dict of field values.

# All rows
rows, errors = strategies.load()

# Filtered by dict — equality matching
rows, errors = strategies.load(where={"status": "LIVE"})

# Filtered by SQL WHERE string — full operator support
rows, errors = strategies.load(where="mechanism >= 7 AND status = 'HYPOTHESIS'")
rows, errors = strategies.load(where="categories LIKE '%defi%'")

The where parameter accepts a dict (equality matching) or a SQL WHERE string (supports =, !=, <, >, <=, >=, LIKE, IN, IS NULL, AND, OR). errors contains any schema validation issues found during loading.

INSERT

# Create a new row — filename derived from title
strategies.insert({
    "title": "My New Strategy",
    "status": "HYPOTHESIS",
    "mechanism": 5,
    "implementation": 4,
    "safety": 7,
    "frequency": 3,
    "composite": 420,
    "categories": ["exchange-structure"],
    "pipeline_stage": "Pre-backtest (step 2 of 9)",
})
# Returns: Path to created file (e.g. my-new-strategy.md)
# created/modified timestamps set automatically
# required sections scaffolded as empty ## headings
# validated against schema before writing

# With pre-formatted body (e.g. from Claude output)
strategies.insert(
    {"title": "Another Strategy", "status": "HYPOTHESIS", ...},
    body=raw_markdown,  # placed verbatim after frontmatter
)

# Overwrite existing file, preserve created timestamp
strategies.insert(
    {"title": "Revised Strategy", "status": "BACKTESTING", ...},
    filename="my-new-strategy",
    replace=True,
)

UPDATE

# Partial merge — only the fields you pass are changed
strategies.update("my-new-strategy.md", {"status": "KILLED", "kill_reason": "No edge"})

# Update body only
strategies.update("my-new-strategy.md", {}, body=new_markdown)

Bulk UPDATE

Table.update_many() updates the same fields across multiple files.

updated_paths = strategies.update_many(
    ["file-a.md", "file-b.md", "file-c.md"],
    {"status": "KILLED"},
)
# Returns: list of paths that were updated

DELETE

strategies.delete("my-new-strategy.md")

Schema operations

table = Table("examples/strategies/")

table.rename_field("Summary", "Overview")     # section or frontmatter
table.drop_field("Details")                   # section or frontmatter
table.merge_fields(["Entry Rules", "Exit Rules"], into="Trading Rules")  # sections only

Validation

errors = strategies.validate()
# Returns: list of validation errors (schema + FK)

All writes are validated against the schema and rolled back on failure. The created timestamp is always preserved on replace and update; modified is always set to today.

CLI commands

mdql query <folder> "<sql>"

Run SQL against a table or database. Supports SELECT, INSERT INTO, UPDATE SET, DELETE FROM, ALTER TABLE, and JOIN.

# Filter and sort
mdql query examples/strategies/ \
  "SELECT title FROM strategies WHERE mechanism > 5 ORDER BY composite DESC LIMIT 5"

# Query section content
mdql query examples/strategies/ \
  "SELECT path, Hypothesis FROM strategies WHERE Hypothesis IS NOT NULL LIMIT 3"

# Category search (LIKE works on arrays)
mdql query examples/strategies/ \
  "SELECT title FROM strategies WHERE categories LIKE '%defi%'"

# Output as JSON
mdql query examples/strategies/ \
  "SELECT title, composite FROM strategies LIMIT 3" --format json

Supported WHERE operators: =, !=, <, >, <=, >=, LIKE, IN, IS NULL, IS NOT NULL, AND, OR

Column names with spaces use backticks: SELECT `Structural Mechanism` FROM strategies

JOINs

Point at the database directory (parent of table folders) for cross-table queries. Supports two or more tables:

# Two-table JOIN
mdql query examples/ \
  "SELECT s.title, b.sharpe, b.status
   FROM strategies s
   JOIN backtests b ON b.strategy = s.path"

# Multi-table JOIN
mdql query my-db/ \
  "SELECT s.title, b.result, c.verdict
   FROM strategies s
   JOIN backtests b ON b.strategy = s.path
   JOIN critiques c ON c.strategy = s.path"

SQL write operations

# INSERT
mdql query examples/strategies/ \
  "INSERT INTO strategies (title, status, mechanism, implementation, safety, frequency, composite, categories, pipeline_stage)
   VALUES ('New Strategy', 'HYPOTHESIS', 5, 4, 7, 3, 420, 'exchange-structure', 'Pre-backtest')"

# UPDATE
mdql query examples/strategies/ \
  "UPDATE strategies SET status = 'KILLED', kill_reason = 'No edge' WHERE path = 'new-strategy.md'"

# DELETE
mdql query examples/strategies/ \
  "DELETE FROM strategies WHERE path = 'new-strategy.md'"

For string[] columns, pass comma-separated values in a single string: 'funding-rates,defi'.

ALTER TABLE — field migrations

Rename, drop, or merge fields across all files in a table. Works for both frontmatter fields and sections. The schema _mdql.md is updated automatically.

mdql query examples/strategies/ \
  "ALTER TABLE strategies RENAME FIELD 'Summary' TO 'Overview'"
# ALTER TABLE — renamed 'Summary' to 'Overview' in 42 files

mdql query examples/strategies/ \
  "ALTER TABLE strategies DROP FIELD 'Details'"

mdql query examples/strategies/ \
  "ALTER TABLE strategies MERGE FIELDS 'Entry Rules', 'Exit Rules' INTO 'Trading Rules'"

Field names can be single-quoted ('Name'), backtick-quoted (`Name With Spaces`), or bare identifiers.

mdql rename <db-folder> <table> <old-name> <new-name>

Rename a file within a table. Automatically updates all foreign key references in other tables that point to the old filename.

mdql rename examples/ strategies bad-debt-socialization-event-token-short.md bad-debt-token-short.md
# Renamed strategies/bad-debt-socialization-event-token-short.md → bad-debt-token-short.md
# Updated 3 references in backtests

mdql create <folder> --set key=value

Create a new row file. Field types are coerced from the schema (e.g. --set mechanism=5 becomes int).

mdql create examples/strategies/ \
  -s 'title=My New Strategy' \
  -s 'status=HYPOTHESIS' \
  -s 'mechanism=5' \
  -s 'implementation=4' \
  -s 'safety=7' \
  -s 'frequency=3' \
  -s 'composite=420' \
  -s 'categories=exchange-structure' \
  -s 'pipeline_stage=Pre-backtest (step 2 of 9)'

For string[] fields, use comma-separated values: -s 'categories=funding-rates,defi'

mdql validate <folder>

Validate all markdown files against the schema. Works on a single table or a database directory.

mdql validate examples/strategies/
# All 100 files valid in table 'strategies'

Invalid files get clear error messages:

missing-field.md: Missing required frontmatter field 'count'
wrong-type-date.md: Field 'created' expected date, got string 'yesterday'
duplicate-section.md: Duplicate section 'Body' (appears 2 times)

When pointed at a database directory, also reports foreign key violations (see Foreign key validation).

mdql inspect <folder>

Show normalized rows.

mdql inspect examples/strategies/ -f bad-debt-socialization-event-token-short.md --format json

mdql stamp <folder>

Add or update created and modified timestamps in all data files.

mdql stamp examples/strategies/
# Stamped 100 files: 0 created set, 100 modified updated

• created is set to today's date if missing, never overwritten
• modified is always updated to today's date
• Both are ISO date strings ("YYYY-MM-DD") in frontmatter
• These fields are reserved — schemas don't need to declare them, and they are never rejected as unknown fields

mdql schema <folder>

Print the effective schema. Works on a single table or the whole database.

mdql schema examples/

mdql repl <folder>

Open an interactive REPL for running queries. Supports tab completion for table names, column names, and SQL keywords.

mdql repl examples/

When pointed at a database directory, runs a background filesystem watcher that prints FK violations to stderr if files change on disk while the REPL is open.

mdql client <folder>

Open a browser-based UI for running queries. Starts a local web server with a query editor.

mdql client examples/

The web server exposes a REST API:

• POST /api/query — execute SQL
• GET /api/fk-errors — current foreign key violations (updated by background watcher)

Pandas integration

pip install mdql[pandas]

One-liner

from mdql.pandas import load_dataframe

df = load_dataframe("examples/strategies/")

Two-step (when you already have rows)

from mdql.loader import load_table
from mdql.pandas import to_dataframe

schema, rows, errors = load_table("examples/strategies/")
df = to_dataframe(rows, schema)

Schema types map to pandas dtypes:

MDQL type	pandas dtype
string	string
int	Int64 (nullable)
float	Float64 (nullable)
bool	boolean (nullable)
date	datetime64[ns]
string[]	Python lists

Validation errors are handled via the errors parameter: "warn" (default), "raise", or "ignore".

ACID compliance

All write operations are process-safe. Three layers of protection:

Atomic writes. Every file write goes through a temp-file-then-rename path. If the process crashes mid-write, the original file is untouched.

Table locking. Write operations acquire an exclusive fcntl.flock per table. Two processes writing to the same table serialize rather than corrupt each other's files.

Write-ahead journal. Multi-file operations (ALTER TABLE, batch UPDATE/DELETE, stamp) write a journal before making changes. If the process crashes mid-operation, the next Table() construction detects the journal and rolls back all partial changes automatically.

# Safe even if the process is killed mid-way:
table.rename_field("Summary", "Overview")  # touches 100 files + schema
# On crash: next Table("strategies/") auto-recovers from journal

Running tests

# Rust tests
cargo test

# Python tests (requires maturin develop first)
pytest

Project structure

crates/
  mdql-core/        # core library: parser, schema, validator, query engine,
                     # indexes, caching, full-text search, ACID transactions,
                     # FK validation, filesystem watcher
  mdql/             # CLI binary: validate, query, create, inspect, schema,
                     # stamp, rename, repl (with autocomplete), client (web UI)
  mdql-web/         # browser UI: axum REST server + embedded SPA
python/
  src/lib.rs        # PyO3 bindings (Rust → Python)
  mdql/             # Python wrapper package (thin layer over Rust)
tests/              # Python test suite
examples/           # example data (strategies, backtests)

License

AGPL-3.0. Commercial licenses available — see LICENSE.md.