SQLGuard Ninja

Security testing, policy enforcement, agent integration, privacy analysis and CI benchmarking for LLM-generated SQL.

When an LLM writes SQL, the system prompt is not a security boundary. SQLGuard Ninja sits between the model and the database. It checks every statement against a declared policy for the authenticated caller: which tables and columns a role may use, which data classes may appear only in aggregates or only after human approval, and which tenant the caller belongs to. It records an audit trail and gives the agent an explanation it can act on.

It ships with a labelled benchmark corpus (551 cases, 1,044 dialect evaluations) and a regression gate for CI. The same benchmark harness can evaluate other open-source guards side by side.

One layer, not the only one. Static SQL inspection cannot guarantee database security. Use a read-only least-privilege role, row-level security and statement timeouts as well. See the threat model.

What it does

Not yet included: governed writes (all writes are denied in v0.1); benchmark cases for restricted functions and system catalogs (the rules exist, but the corpus does not cover them); dialects beyond PostgreSQL and SQLite (they parse, but are untested). Full list: KNOWN_LIMITATIONS.md.

Architecture

flowchart LR
    subgraph App["Your application"]
      Auth["Auth layer"] --> Ctx["RequestContext<br/>(principal, role, tenant)"]
      LLM["LLM / agent"] -->|SQL text| CP
      Ctx --> CP["SQLCheckpoint<br/>block / review / audit"]
    end
    CP --> G["Guard"]
    G --> AN["Analyser<br/>sqlglot qualify + scopes"]
    AN --> R1["Statement / catalog / function rules"]
    AN --> R2["Table and column grants"]
    AN --> R3["Privacy labels"]
    AN --> R4["Tenant pins"]
    AN --> R5["Limits + static cost"]
    CP -->|authorized only| EX["Read-only executor"] --> DB[("Database<br/>grants, RLS, timeouts")]
    CP --> AU["Audit sink<br/>hash + redacted SQL"]
    CP -.review.-> AP["ApprovalQueue (human)"]
    G -.ALLOW only.-> PI["PostgreSQL EXPLAIN inspector"]
    subgraph Bench["Benchmark + CI"]
      DS["Corpus v1"] --> RUN["Runner"] --> ADP["Adapters: native, callable,<br/>isolated external workers"]
      RUN --> RES["Result JSON / Markdown"] --> CMP["Baseline compare"] --> GATE["GitHub Action gate"]
    end

Design decisions and their trade-offs are recorded in ARCHITECTURE_DECISIONS.md.

Five-minute quick start

python -m pip install sqlguard-ninja            # core: sqlglot, pydantic, PyYAML
python -m pip install "sqlguard-ninja[all]"     # + LangChain, LangGraph, FastAPI, psycopg

Extras: langchain, langgraph, fastapi, postgres, all. Python 3.11+.

Validate a query against the bundled reference policy (builtin:retail_saas, a synthetic multi-tenant retail schema):

sqlninja validate --policy builtin:retail_saas --role support_analyst --tenant 1   --sql "SELECT o.id FROM orders o WHERE o.tenant_id = 1 OR 1 = 1"

DENY:
  [deny] tenant.missing_predicate: Every read of table 'orders' must filter on the caller's tenant. Suggestion: Add `o.tenant_id = :tenant_id` to the WHERE clause of the scope that reads this table.

Exit codes: 0 allow, 1 deny, 3 review, 2 usage error.

Run the bundled benchmark corpus, then start your own project:

sqlninja benchmark run --dataset builtin:v1 --output results/native.json
sqlninja init my-project && cd my-project
sqlninja benchmark run --config sqlninja.yaml

The runnable demos live in the repository (deterministic; no API key needed):

git clone https://github.com/Pratik653/SQLGuard_Ninjapy.git && cd SQLGuard_Ninjapy
python -m pip install -e ".[all]"
python examples/sdk/quickstart.py
python examples/sqlite/text_to_sql_demo.py
python examples/langgraph/sql_agent_demo.py

Python SDK

from sqlguard_ninja import Guard, Policy

from sqlguard_ninja.benchmarking.builtin import resolve

guard = Guard(Policy.from_file(resolve("builtin:retail_saas", "policy")))
result = guard.validate(
    "SELECT department, AVG(salary) FROM employees GROUP BY department",
    role="hr_analyst",
    dialect="postgres",
)
result.allowed      # True
result.findings     # () - structured Finding objects with rule_id, action, message, remediation

guard.validate("SELECT full_name, salary FROM employees", role="hr_analyst").explain()
# DENY:
#   [deny] privacy.aggregate_only: The column 'employees.salary' may only be used inside
#   statistical aggregates (COUNT, SUM, AVG, ...), not as individual values. ...

LangGraph

from sqlguard_ninja.integrations import RequestContext, SQLCheckpoint
from sqlguard_ninja.integrations.langgraph import (
    CONTEXT_KEY, make_execute_node, make_guard_node, route_after_guard)

checkpoint = SQLCheckpoint(guard, mode="block", max_denied_attempts=3)
graph.add_node("guard", make_guard_node(checkpoint))
graph.add_node("execute", make_execute_node(checkpoint, executor))   # re-validates
graph.add_conditional_edges("guard", route_after_guard(3),
                            {"execute": "execute", "revise": "generate", "end": END})

ctx = RequestContext(principal=user.id, role=user.role, tenant_id=user.tenant_id)
app.invoke(state, config={"configurable": {CONTEXT_KEY: ctx}})       # nodes cannot alter config

More in AGENT_INTEGRATION.md: the LangChain tool (its schema accepts only query), the FastAPI router, review-mode approvals and audit sinks.

Privacy policies

Sensitivity comes from labels you assign in the policy, never from column names, and access is resolved per role:

labels:
  payment_card: {sensitivity: critical, masking: use card_last4 and card_brand}
  financial:    {sensitivity: high}
catalog:
  tables:
    payments:
      tenant_column: tenant_id
      columns:
        card_number: {labels: [payment_card], alternatives: [card_last4]}
        card_last4: text
roles:
  support_analyst:
    tables: {payments: [id, tenant_id, card_last4, card_brand, amount, status]}
    labels: {payment_card: deny, financial: deny}
  hr_analyst:
    tables: {employees: "*"}
    labels: {hr: allow, financial: aggregate_only}   # salary only inside COUNT/SUM/AVG

support_analyst> SELECT p.card_number FROM payments p WHERE p.tenant_id = 1
DENY:
  [deny] privacy.label_denied: The column 'payments.card_number' contains classified data (payment_card) that this role may not access. Suggestion: Use column 'payments.card_last4' instead. ...

hr_analyst> SELECT AVG(salary) FROM employees WHERE id = 7
REVIEW:
  [review] privacy.small_cohort: An aggregate of restricted data is filtered or grouped by an identifying column, which can reveal individual values. ...

Labels also apply to paths inside JSON columns (profile->'health'->>'allergies'). sqlninja policy suggest proposes labels from column names for a human to review; those suggestions are never enforced. This is a technical control, not a certification of GDPR compliance. Full semantics: POLICY_REFERENCE.md.

Policy as code

Roles can inherit (extends), and explicit denies cannot be relaxed by a child. Every decision carries the policy revision, the policy fingerprint and a decision id. Review changes before activating them:

sqlninja policy template multi_tenant_saas --output policy.yaml
sqlninja policy diff old.yaml policy.yaml --fail-on-relaxation
sqlninja policy simulate --policy old.yaml --against policy.yaml --cases cases.yaml
sqlninja policy explain --policy policy.yaml --role support --column customers.email

Optional: SQLCheckpoint(..., rewrite_tenant_filters=True) adds missing tenant filters through the AST and executes only the re-validated rewrite. See POLICY_AS_CODE.md.

MCP server

Let MCP-compatible agents check SQL against your policy before running it anywhere:

python -m pip install "sqlguard-ninja[mcp]"
sqlninja mcp --policy builtin:retail_saas --role support_analyst --tenant 1

The four tools are validate_sql, explain_policy_decision, inspect_query_cost and get_policy_capabilities. The role and tenant are fixed server-side, the server never connects to a database, and it exposes no execution tool. Tested with the official MCP Python SDK client over stdio. See MCP_INTEGRATION.md.

Query cost analysis

Every validation includes an explainable static score that uses the catalog's estimated_rows:

platform_admin> SELECT o.id, i.id FROM orders o CROSS JOIN order_items i
DENY:
  [deny] cost.static_score: Estimated query cost risk is 100/100: join with i has no join condition (Cartesian product); o has an estimated 10,000,000 rows and is read without a filter; ...

Optionally, compare it with PostgreSQL's planner. This runs EXPLAIN (FORMAT JSON) only, never ANALYZE, and only on SQL the guard allowed, inside a read-only, time-limited, rolled-back transaction:

from sqlguard_ninja.query_cost.postgres import PostgresPlanInspector
report = PostgresPlanInspector(guard, lambda: psycopg.connect(READER_DSN)).inspect(
    sql, role="support_analyst", context={"tenant_id": 1})
report.total_cost, report.plan_rows, report.static.score, report.findings

See QUERY_COST.md and examples/postgresql/plan_inspection_demo.py.

Benchmark

sqlninja benchmark run --dataset builtin:v1 --adapter native
python scripts/setup_external_adapters.py          # (repository) isolated venvs for other tools
sqlninja benchmark run --dataset builtin:v1 --adapter external:sql-guardrail
sqlninja benchmark compare --baseline benchmarks/baselines/native.json --candidate results/latest.json

Results for corpus v1.1.0 (551 cases, 1,044 evaluations; SQLGuard Ninja 0.2.0; Windows 11, Python 3.11). Intervals are 95% Wilson intervals. Details, CSV and raw files: RESULTS_v1.1.md.

All of these are internal results. The corpus was written by this project, alongside the engine. The native 100% shows consistency with the documented semantics, not independent detection quality. No independently sourced dataset exists yet (intake rules, issue #6). Reports keep internal and independent tiers separate, and they also separate policy denials from unsupported-SQL denials. Methodology and bias review: BENCHMARK_METHODOLOGY.md, BENCHMARK_BIAS_REVIEW.md.

How it relates to existing tools

SQLGuard Ninja uses sqlglot for parsing, dialects and scope analysis, and does not re-implement them. sql-guardrail is a thorough read-only validator with a tautology catch-all, which this project does not duplicate. agent-sql-guard has a careful schema-less PII denylist. What SQLGuard Ninja adds: role- and label-based policies, the agent checkpoint contract, a shared benchmark with isolated adapters, planner inspection, and the CI gate. Full comparison: COMPETITIVE_ANALYSIS.md.

Security limitations

• Static inspection can be wrong where sqlglot and the real database parse SQL differently. Only PostgreSQL and SQLite are tested.
• It cannot see inside views or user-defined functions, and it does not stop inference across many permitted queries.
• Cost scores and planner estimates are indicators, not guarantees.
• v0.1 denies all writes.
• The benchmark has no restricted-function or system-catalog cases yet. The rules exist, but those two categories are not measured.

Use database grants, row-level security and timeouts as the authoritative controls. See the threat model, limits of static analysis, the benchmark bias review and KNOWN_LIMITATIONS.md.

Roadmap

Next: restricted-function and system-catalog benchmark cases, an independent held-out corpus, lineage-aware aggregate checks, and tenant predicate push-down. Later: governed writes, more tested dialects, and SARIF output. Details in ROADMAP.md.

Links

• Repository: https://github.com/Pratik653/SQLGuard_Ninjapy
• Releases: https://github.com/Pratik653/SQLGuard_Ninjapy/releases
• PyPI: https://pypi.org/project/sqlguard-ninja/
• Issues: https://github.com/Pratik653/SQLGuard_Ninjapy/issues
• Security policy: SECURITY.md · Contributing: CONTRIBUTING.md

Documentation

• Policy reference
• Policy as code
• MCP integration
• Agent integration
• Query cost
• CI integration
• Benchmark methodology
• Threat model
• Limits of static SQL analysis and dialect support
• Benchmark bias review
• Architecture decisions
• Known limitations · Roadmap · Changelog

Supported versions

• Python 3.11, 3.12, 3.13 (CI matrix on Linux and Windows).
• SQL dialects: PostgreSQL (tested against PostgreSQL 16) and SQLite. Other sqlglot dialects parse but are experimental and untested.

Development

python -m pip install -e ".[dev]"
ruff check src tests scripts examples && ruff format --check src tests scripts examples
mypy
pytest                          # PostgreSQL tests run if SQLNINJA_PG_DSN is set or pgserver is installed
python scripts/generate_corpus.py --check

See CONTRIBUTING.md. Report vulnerabilities privately per SECURITY.md.

Licence

Apache-2.0. No third-party code is vendored; dependencies and their licences are listed in THIRD_PARTY_NOTICES.md. All benchmark data is synthetic.