exmergo-dex-core

The portable, Apache-2.0 analytics-engineering engine behind Dex. All non-trivial logic lives here; the Claude Code skills and the cross-agent AGENTS.md are thin wrappers that drive it through one stable command contract.

Dex is the agent-native analytics engineering toolkit: explore an unfamiliar warehouse, transform raw data into clean dbt models and a semantic layer on top, and maintain all of it as the data underneath changes. Read-only against your data; every change is a reviewable diff.

Install

pip install "exmergo-dex-core"

Connector client libraries live behind extras. DuckDB is an in-memory data warehouse, so you can start from there if you want to test Dex locally. We aim to support all major data warehouses. Please suggest any missing connectors on GitHub!

exmergo-dex-core[duckdb]       # the on-ramp and the eval/benchmark engine
exmergo-dex-core[snowflake]
exmergo-dex-core[bigquery]
exmergo-dex-core[databricks]
exmergo-dex-core[redshift]
exmergo-dex-core[postgres]
exmergo-dex-core[all]          # every connector at once

Two surfaces, one engine

The Python API

from exmergo_dex_core import DexEngine

with DexEngine(connector="duckdb", path="shop.duckdb") as eng:
    mapped = eng.map()
    rows = eng.query("select status, count(*) from orders group by status")

Methods return domain objects (DexCache, Dataset, Snapshot) and result records carrying the counts, notes, and warnings that explain them. The stdout envelope never crosses this boundary.

Nothing above touches disk. The default store keeps state in the process, so importing this package cannot leave a .dex/ directory in a consumer's repo; pass store= for anything durable, or use DexEngine.from_repo(repo_root) to get the CLI's behavior (filesystem store, config read from .dex/config.yml). The Store protocol is public, so a host can back state with its own session store or database instead.

examples/quickstart.py is the whole flow in one runnable file: map a warehouse, read the inferred joins, see PII flagged, ask a question, and watch the firewall refuse one it should. It builds its own throwaway DuckDB file, so it runs anywhere:

pip install "exmergo-dex-core[duckdb]"
python quickstart.py

The test suite runs that file against a freshly built wheel, so the usage documented here is the usage that is verified.

Every guarantee below holds here too, because it is the same code. An unconfirmed billed call raises ConfirmationRequiredError carrying the estimate and the payload needed to re-issue; an over-ceiling one raises OverCeilingError and cannot be confirmed through.

Three rules matter the moment a process serves more than one user, and all three are in DexEngine's docstring: scope one engine to one principal and one session, know that an engine given an explicit config= never reads one from disk (so a stray .dex/config.yml above the working directory cannot silently supply someone else's connector, budget, or PII overrides), and supply the connection when the request's identity is not the container's.

That last one is what makes per-end-user access control expressible. By default dex discovers the credential from process-ambient state, which is right for one person at a terminal and process-wide everywhere else. Pass a ConnectionSource and the host owns authentication:

from exmergo_dex_core import ConnectionSource, DexEngine

with DexEngine(
    connector="snowflake",
    config=cfg,
    store=store,
    connection=ConnectionSource(connect=lambda: user_conn),
) as eng:
    eng.inventory()

It is a zero-argument factory rather than a live connection, so a free metadata command never opens a billed session. Two things stay dex's. The cost gate is still built here from your store, so the per-command ceiling and the cumulative session ceiling bind exactly as they do on a discovered connection; handing that to an integrator would let a fumbled figure disarm the brake in the deployment where a runaway agent loop costs the most. And dex closes nothing it reached through the source, because the caller that opened a connection is the one still holding it. Nothing is persisted either way: dex never stores, caches, or refreshes a credential.

A hosted dbt Cloud Semantic Layer is a second service with its own credential, so it has its own parameter. Non-secret coordinates go in the config, where they can be committed; the service token never can, so it arrives separately:

from exmergo_dex_core import DexConfig, DexEngine, SemanticSource

config = DexConfig(
    semantic={"backend": "dbt_cloud", "host": host, "environment_id": env_id}
)

with DexEngine(
    config=config,
    semantic_source=SemanticSource(token=lambda: token_for(user)),
) as eng:
    catalog = eng.semantic_list()
    result = eng.semantic_query("revenue", group_by=["metric_time__month"])

That is the one surface needing nothing on the filesystem at all: no dbt project, no store, no connector, no credential file. The token callable runs once per semantic command rather than once per HTTP request, so a metric query that polls dbt Cloud while it runs costs you one token read. Note that dbt Cloud owns the warehouse connection on this path and executes server-side, so dex's cost guard cannot apply and every hosted result says so; the PII dimension gate still does.

The command contract

Every subcommand prints exactly one sanitized JSON envelope to stdout and nothing else; nothing reaches agent context except through that envelope. Credentials never cross it, and data values cross only from profiled, PII-cleared columns, bounded and capped by the query firewall. State persists in .dex/, so subcommands are stateless and the agent orchestrates multi-step flows.

dex connect test --path data.duckdb

The CLI is the API's first consumer rather than a parallel implementation: it parses arguments, builds an engine, and wraps the result it gets back. See references/command-contract.md for the full surface and the envelope spec.

Status

Early and under active development; open issues on GitHub! Today the engine runs Explore, Transform, and Maintain end to end on every connector: DuckDB, BigQuery, Snowflake, Databricks, Amazon Redshift, and Postgres, through either the command contract or the Python API.

Commands

explore: ranks what matters in an unfamiliar warehouse, profiles columns selectively, flags PII, surfaces grain and data-quality warnings, infers joins and verifies them with overlap probes (--verify), and executes agent-authored ad-hoc SELECTs behind a PII-aware query firewall (explore query), all read-only. It starts bare by default; with --use-project it reads an existing dbt project, promoting declared relationships joins, honoring declared grain and unique tests, and letting metric-backing models surface first in the ranking. A repeatable --scope narrows the source scope per command without writing back to .dex/config.yml. It also queries the dbt semantic layer (explore semantic list / query): metric queries run either locally through MetricFlow and dex's own cost handshake (--local), or against a hosted dbt Cloud deployment (--api), where dbt Cloud executes server-side and every result warns that dex's cost guard does not apply there.

transform: bootstraps a dbt project where none exists (transform init, with an explicit connector, never a default), turns agent-authored edits and deterministic staging scaffolds into reviewable, conflict-checked diffs (transform plan / apply, with human edits authoritative on conflict), runs gated dev-target-only builds with cost surfaced before any spend (transform build), and authors the semantic layer as MetricFlow-validated dbt semantic models (semantic define|update|plan, applied with transform apply).

maintain: detects drift against the .dex/ snapshot on four axes and proposes the fix: schema (structure), volume (freshness), grain (uniqueness and fanout), and semantic (definitions, dangling references, and dimension cardinality). maintain check sweeps all of them, ranked by blast radius; reconcile proposes reviewable diffs tagged mechanical or advisory, applied through transform apply. Detection is read-only on every connector; on billed connectors the metadata axes (schema, volume, references) stay free while the scanning axes (grain, dimension cardinality) take the --confirm --budget handshake, so check is two-phase.

Connectors

Every connector below discovers its own credentials and never asks for a key or a password, which is the right default for a CLI one person runs. A process serving several end users supplies the connection instead (see the Python API above), and dex still builds the cost gate, narrows scope inward only, and keeps the session read-only. The connector extra is required either way, since each adapter reads its driver's error types to translate refusals.

BigQuery: connects through Application Default Credentials (gcloud auth application-default login; dex discovers credentials, it never asks for keys). Metadata is free; every scan is dry-run first, returned as a needs_confirmation estimate, and runs only with --confirm --budget <bytes>, capped server-side by maximum_bytes_billed and recorded in a local .dex/spend.jsonl ledger. dbt builds go to a dedicated dev dataset via dbt-bigquery, which the [bigquery] extra carries. See references/bigquery.md.

Snowflake: connects through discovered credentials (connections.toml, SNOWFLAKE_* env, or a dbt profile; dex never asks for or persists a password). The cost inversion from BigQuery: metadata is free (SHOW commands, no warehouse), while scans bill warehouse time, so budgets are warehouse-seconds with credits shown alongside. Estimates are an honestly labeled heuristic (Snowflake has no dry-run), floored by the 60-second resume minimum on a cold warehouse; the budget is hard-enforced anyway by a per-statement server-side STATEMENT_TIMEOUT_IN_SECONDS, and actual seconds land in the same .dex/spend.jsonl ledger. Billed work runs only on the warehouse the config pins. dbt builds go to a dedicated dev database.schema via dbt-snowflake, which the [snowflake] extra carries. See references/snowflake.md.

Databricks: the lakehouse connector. Connects through the Databricks SDK's unified auth chain (databricks auth login, DATABRICKS_* env, or a dbt profile; dex never asks for or persists a token). Metadata is free through the Unity Catalog REST API, and the SQL session opens lazily on the first billed statement, so free commands never touch (or wake) the warehouse. Budgets are warehouse-seconds with DBUs shown alongside. Estimates start as an honestly labeled floor (no dry-run, no free table sizes) and refine in-budget via DESCRIBE DETAIL; the budget is hard-enforced anyway by a per-statement server-side STATEMENT_TIMEOUT, and actual seconds land in the same .dex/spend.jsonl ledger. Billed work runs only on the SQL warehouse the config pins. dbt builds go to a dedicated dev catalog.schema via dbt-databricks, which the [databricks] extra carries. See references/databricks.md.

Amazon Redshift: Serverless-first and provisioned-compatible. Connects through the AWS default credential chain (a pinned Serverless workgroup or provisioned cluster_identifier mints IAM temporary database credentials), the REDSHIFT_* environment, the committed non-secret target (password via REDSHIFT_PASSWORD), or a dbt profile; dex never asks for or persists a password. Metadata comes from the Postgres catalog (pg_class merged with SVV_TABLE_INFO and SVV_COLUMNS, so empty tables still appear). The guarded quantity is compute time, so budgets are compute-seconds with RPU-hours shown alongside (dollars when redshift.rpu_price_usd is set), floored once by the 60-second Serverless wake minimum; the budget is hard-enforced by a per-statement server-side statement_timeout, and actual seconds land in the same .dex/spend.jsonl ledger. Profiling uses HLL(...) approximate distincts with exact escalation in-budget; the session is read-only at the server. dbt builds go to a dedicated dev schema via dbt-redshift, which the [redshift] extra carries. See references/redshift.md.

PostgreSQL: the operational-database connector. Connects through discovered credentials (pg_service.conf, DATABASE_URL, the PG* environment, or a dbt profile; dex never asks for or persists a password). Nothing is billed in dollars; the guarded quantity is load on what is often a production primary, so budgets are database-seconds through the same confirm handshake. Query estimates come from the genuinely free planner preflight (EXPLAIN), profile estimates from relation sizes, both labeled heuristic; the budget is hard-enforced anyway by a per-statement server-side statement_timeout, and actual seconds land in the same ledger. The session is read-only at the server (default_transaction_read_only = on), profiling leans on the planner's own statistics instead of scanning distincts, and dbt builds go to a dedicated dev schema via dbt-postgres, which the [postgres] extra carries, with the ceiling injected as a statement timeout through PGOPTIONS. See references/postgres.md.

License

Apache-2.0.