MMDB Forge

MMDB Forge is a developer toolkit for inspecting, validating, diffing, and explaining custom MaxMind DB files.

Most MaxMind DB tools are built around one question:

What does this IP resolve to?

MMDB Forge is built for people who generate, ship, and maintain their own .mmdb files. It helps answer the questions that matter before a database release goes to production:

What changed between two versions?
Did the schema break?
Why did this IP get this record?
Which fields disappeared?
How many prefixes changed country, ASN, VPN status, confidence, or risk score?
Where did confidence suddenly become 0?
Which records became null?
Did the file become much larger?
Do known test IPs still return the expected values?

Think of it as jq + diff + validator + CI guardrails for .mmdb releases.

What It Does

MMDB Forge is both a CLI and a small Go codebase organized around MMDB release quality checks.

It can:

inspect a single IP lookup with the matched network prefix
explain why a record matched and surface suspicious record details
compare old and new database versions on sampled records or a fixed IP list
validate records against a simple JSON schema
list all observed fields in a database
calculate field coverage and top values
run smoke tests for known IP expectations
run a full release audit that combines diff, stats, schema validation, and smoke tests

Install

From source:

git clone https://github.com/ipanalytics/MMDBForge.git
cd mmdbforge
go build ./cmd/mmdbforge

Install the local checkout into your GOBIN:

go install ./cmd/mmdbforge

Check the CLI:

mmdbforge --help

Quick Start

Inspect an IP:

mmdbforge inspect vpn.mmdb 91.196.220.30

Compare two releases:

mmdbforge diff vpn-2026-05-20.mmdb vpn-2026-05-21.mmdb --sample 100000

Validate records against a schema:

mmdbforge validate examples/vpn.schema.json vpn.mmdb --sample 50000

Run a release audit:

mmdbforge audit release \
  --old vpn-2026-05-20.mmdb \
  --new vpn-2026-05-21.mmdb \
  --schema examples/vpn.schema.json \
  --smoke examples/smoke.json \
  --sample 100000 \
  --markdown report.md

Commands

mmdbforge inspect <db.mmdb> <ip>
mmdbforge explain <db.mmdb> <ip>
mmdbforge explain-diff <old.mmdb> <new.mmdb> <ip>
mmdbforge lint cidr <prefixes.txt|prefixes.csv|prefixes.jsonl>
mmdbforge diff <old.mmdb> <new.mmdb> [flags]
mmdbforge validate <schema.json> <db.mmdb> [flags]
mmdbforge stats <db.mmdb> [flags]
mmdbforge stats diff <old.mmdb> <new.mmdb> [flags]
mmdbforge fields <db.mmdb> [flags]
mmdbforge smoke <db.mmdb> <smoke.json>
mmdbforge test run <config.yaml> [--output run.json]
mmdbforge test compare <baseline.json> <current.json> [--output compare.json]
mmdbforge test report <compare.json> [--markdown [file]] [--html [file]]
mmdbforge prefixes <db.mmdb> [new.mmdb] [flags]
mmdbforge bench <db.mmdb> [new.mmdb] [flags]
mmdbforge audit release --old <old.mmdb> --new <new.mmdb> [flags]

All commands print pretty JSON by default. diff and audit release can also write Markdown reports.

inspect

inspect performs a lookup and returns the record together with the matched network prefix.

mmdbforge inspect vpn.mmdb 91.196.220.30

Example output:

{
  "ip": "91.196.220.30",
  "database": "vpn.mmdb",
  "matched_prefix": "91.196.220.30/32",
  "record": {
    "privacy": {
      "is_vpn": true,
      "vpn_provider": "NordVPN",
      "is_hosting": true
    },
    "confidence": 95
  }
}

Use it when you want a direct, debuggable lookup without writing a small Go program or piping raw data through another tool.

explain

explain shows the lookup result plus useful context about the matched record.

mmdbforge explain vpn.mmdb 91.196.220.30

Example output:

{
  "ip": "91.196.220.30",
  "database": "vpn.mmdb",
  "matched_prefix": "91.196.220.30/32",
  "prefix_length": 32,
  "record_size_bytes": 384,
  "fields": [
    "privacy.is_vpn",
    "privacy.vpn_provider",
    "privacy.is_hosting",
    "confidence"
  ],
  "warnings": [
    "matched host-level record; check if this database intentionally stores host-level entries"
  ],
  "record": {
    "privacy": {
      "is_vpn": true,
      "vpn_provider": "NordVPN",
      "is_hosting": true
    },
    "confidence": 95
  }
}

This is useful when a generated database has unexpected host-level records, missing risk explanation fields, or confidence values outside the expected range.

diff

diff is the main release-safety command.

It samples records from the old database, looks up the same IPs in the new database, and reports record-level and field-level changes.

mmdbforge diff old.mmdb new.mmdb --sample 100000

Example output:

{
  "sample_size": 100000,
  "changed_records": 8421,
  "changed_percent": 8.42,
  "field_changes": {
    "privacy.is_vpn": {
      "false_to_true": 1203,
      "true_to_false": 312
    },
    "privacy.vpn_provider": {
      "changed": 842,
      "added": 1203,
      "removed": 312
    },
    "network_context.geo_country_code": {
      "changed": 91
    }
  },
  "top_changes": [
    {
      "field": "privacy.vpn_provider",
      "old": null,
      "new": "NordVPN",
      "count": 433
    },
    {
      "field": "network_context.geo_country_code",
      "old": "GB",
      "new": "US",
      "count": 28
    }
  ],
  "failed": false
}

Useful flags:

--sample 100000
--full
--ips test-ips.txt
--fields privacy.is_vpn,privacy.vpn_provider
--json
--markdown
--markdown report.md
--fail-on-change privacy.is_vpn
--fail-on-drop confidence
--fail-on-missing-field confidence
--fail-threshold changed_percent=20

Examples:

mmdbforge diff old.mmdb new.mmdb \
  --sample 100000 \
  --fields privacy.is_vpn,privacy.vpn_provider,confidence

mmdbforge diff old.mmdb new.mmdb \
  --ips fixtures/release-check-ips.txt \
  --fail-on-change privacy.is_vpn

mmdbforge diff old.mmdb new.mmdb \
  --sample 100000 \
  --fail-threshold changed_percent=25 \
  --fail-on-missing-field confidence

diff is intentionally sampling-based by default. For very large databases, this gives a fast release signal without requiring a full exhaustive comparison. For deterministic checks, pass a fixed IP list with --ips. For exhaustive database traversal, use --full.

explain-diff

explain-diff explains exactly what changed for one IP between two database versions.

mmdbforge explain-diff old.mmdb new.mmdb 91.196.220.30

It returns the old matched prefix, new matched prefix, old record, new record, and a sorted list of changed dotted fields. This is the fastest way to debug a single customer-reported IP or a smoke-test regression.

lint cidr

lint cidr checks raw source prefixes before they are compiled into MMDB.

mmdbforge lint cidr prefixes.txt
mmdbforge lint cidr prefixes.csv
mmdbforge lint cidr prefixes.jsonl

Supported input:

plain text: first token is CIDR
CSV/TSV: first column is CIDR
JSONL: cidr, network, or prefix string field

It reports invalid CIDRs, duplicate CIDRs, and narrower prefixes shadowed by a broader prefix. This catches source data mistakes that are hard to reconstruct after the database has already been compiled.

validate

validate checks sampled records against a JSON schema.

mmdbforge validate examples/vpn.schema.json vpn.mmdb --sample 50000

Schema example:

{
  "required": [
    "privacy.is_vpn",
    "confidence"
  ],
  "fields": {
    "privacy.is_vpn": {
      "type": "boolean"
    },
    "privacy.vpn_provider": {
      "type": ["string", "null"]
    },
    "confidence": {
      "type": "integer",
      "minimum": 0,
      "maximum": 100
    },
    "risk_score": {
      "type": "integer",
      "minimum": 0,
      "maximum": 100
    }
  },
  "rules": [
    {
      "if": "privacy.is_vpn == true",
      "then_required": ["privacy.privacy_service"]
    },
    {
      "if": "risk_score >= 80",
      "then_required": ["risk_reasons"]
    }
  ]
}

Example output:

{
  "checked_records": 50000,
  "errors": [
    {
      "ip": "91.196.220.30",
      "matched_prefix": "91.196.220.30/32",
      "field": "risk_reasons",
      "message": "risk_score >= 80 requires risk_reasons"
    }
  ]
}

Supported schema features:

required: dotted field paths that must exist
type: string, integer, number, boolean, object, array, null
minimum and maximum for numeric fields
rules: simple conditional requirements using ==, !=, >, >=, <, <=

The schema format is deliberately small. It is meant for MMDB release contracts, not for modeling every possible JSON Schema feature.

MMDB Forge also accepts a basic JSON Schema-style object with required and nested properties. Nested properties are flattened into dotted MMDB field paths before validation.

stats

stats summarizes metadata, file size, field coverage, and top scalar values.

mmdbforge stats vpn.mmdb --sample 10000 --top 10

Example output:

{
  "database_type": "ipanalytics-vpn",
  "ip_version": ["ipv4", "ipv6"],
  "build_epoch": 1779364800,
  "node_count": 1842201,
  "file_size_mb": 96.4,
  "checked_records": 10000,
  "field_coverage": {
    "privacy.is_vpn": 100.0,
    "privacy.vpn_provider": 84.2,
    "confidence": 99.9,
    "risk_reasons": 22.1
  },
  "top_values": {
    "privacy.vpn_provider": [
      ["NordVPN", 1204],
      ["Surfshark", 881],
      ["ExpressVPN", 604]
    ],
    "network_context.connection_type": [
      ["hosting", 9012],
      ["residential", 552]
    ]
  }
}

Use stats when you want to know whether a release changed shape even before looking at exact field transitions.

Compare field coverage between two releases:

mmdbforge stats diff old.mmdb new.mmdb --sample 100000
mmdbforge stats diff old.mmdb new.mmdb --full
mmdbforge stats diff old.mmdb new.mmdb --sample 100000 --table

fields

fields lists every dotted field path observed in sampled records.

mmdbforge fields vpn.mmdb --sample 10000

Example output:

{
  "checked_records": 10000,
  "fields": [
    "confidence",
    "network_context.geo_country_code",
    "privacy.is_hosting",
    "privacy.is_vpn",
    "privacy.vpn_provider",
    "risk_reasons",
    "risk_score"
  ]
}

This is useful when creating a schema for an existing database or investigating whether a generator accidentally renamed or removed fields.

smoke

smoke runs regression tests for known IPs.

mmdbforge smoke vpn.mmdb examples/smoke.json

Smoke file:

[
  {
    "ip": "91.196.220.30",
    "expect": {
      "privacy.is_vpn": true,
      "privacy.vpn_provider": "NordVPN"
    }
  },
  {
    "ip": "8.8.8.8",
    "expect": {
      "profile.is_anycast": true
    }
  }
]

Example output:

{
  "checked": 2,
  "passed": 1,
  "failed": 1,
  "results": [
    {
      "ip": "91.196.220.30",
      "passed": true
    },
    {
      "ip": "8.8.8.8",
      "passed": false,
      "failures": [
        {
          "field": "profile.is_anycast",
          "expected": true,
          "actual": false,
          "message": "value mismatch"
        }
      ]
    }
  ]
}

Smoke tests are best for high-value examples: known VPN exits, known residential IPs, known anycast IPs, test prefixes, internal fixtures, and customer-reported edge cases.

Smoke cases support exact expectations, allowed value sets, and denied value sets:

{
  "ip": "91.196.220.30",
  "expect": {
    "privacy.is_vpn": true,
    "privacy.vpn_provider": "NordVPN"
  },
  "allow": {
    "geo.city_name": ["Los Angeles", "London"]
  },
  "deny": {
    "privacy.vpn_provider": [null, ""]
  }
}

test

test is the MMDB Forge testbench. It turns golden IP samples into reusable release artifacts.

Run a testbench config:

mmdbforge test run examples/ipbench.yaml --output baseline.json

Run it again for a new database version:

mmdbforge test run examples/ipbench.yaml --output current.json

Compare two runs:

mmdbforge test compare baseline.json current.json --output compare.json

Generate reports:

mmdbforge test report compare.json --markdown testbench.md
mmdbforge test report compare.json --html testbench.html

Config example:

name: vpn-release-golden-samples
database: vpn.mmdb
fields:
  - privacy.is_vpn
  - privacy.vpn_provider
  - network.connection_type
  - geo.city_name
cases:
  - ip: 91.196.220.30
    expect:
      privacy.is_vpn: true
      privacy.vpn_provider: NordVPN
      network.connection_type: hosting
    allow:
      geo.city_name:
        - Los Angeles
        - London
    deny:
      privacy.vpn_provider:
        - ""
        - null

This is the “unit tests for IP intelligence databases” layer: exact expected fields, tolerated alternatives, forbidden values, persistent run artifacts, run comparison, and HTML/Markdown reports.

prefixes

prefixes checks prefix-shape distribution and warns when host-level records dominate the sampled networks.

mmdbforge prefixes vpn.mmdb --sample 100000 --table
mmdbforge prefixes vpn.mmdb --full
mmdbforge prefixes old.mmdb new.mmdb --sample 100000

This catches release mistakes such as unexpected /32 or /128 explosions. Compiled MMDB data is already stored as a search trie, so this is a release shape check for the built database rather than a raw source CIDR overlap linter.

bench

bench measures sampled lookup throughput.

mmdbforge bench vpn.mmdb --sample 100000 --table
mmdbforge bench vpn.mmdb --full
mmdbforge bench old.mmdb new.mmdb --sample 100000

Use it to catch releases that become significantly slower even when schema and smoke tests pass.

audit release

audit release combines the core release checks into one command.

mmdbforge audit release \
  --old vpn-2026-05-20.mmdb \
  --new vpn-2026-05-21.mmdb \
  --schema examples/vpn.schema.json \
  --smoke examples/smoke.json \
  --policy examples/release.policy.json \
  --sample 100000 \
  --markdown report.md \
  --html report.html

It runs:

metadata and file size checks
sampled diff
field coverage stats
field coverage diff
prefix-shape checks
lookup benchmark comparison
release policy gates
standalone Markdown and HTML reports
schema validation
known IP smoke tests
release verdict generation

Markdown output example:

# MMDB Release Audit

Verdict: WARN

- 8.42% sampled records changed
- file size changed 4.80%
- schema validation errors: 0
- smoke tests failed: 0

Verdicts:

PASS: no configured checks failed
WARN: suspicious but not contract-breaking changes, such as a large file size increase
FAIL: schema validation or smoke tests failed

Policy example:

{
  "max_changed_percent": 25,
  "max_file_growth_percent": 50,
  "max_lookup_slowdown_percent": 25,
  "max_host_level_growth_percent": 50,
  "required_fields": [
    "privacy.is_vpn",
    "confidence"
  ],
  "allowed_dropped_fields": []
}

CI Example

MMDB Forge is designed to be useful in CI.

name: MMDB release checks

on:
  pull_request:
  workflow_dispatch:

jobs:
  audit:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: actions/setup-go@v5
        with:
          go-version: "1.22"

      - name: Install mmdbforge
        run: go install ./cmd/mmdbforge

      - name: Audit MMDB release
        run: |
          mmdbforge audit release \
            --old artifacts/vpn-previous.mmdb \
            --new artifacts/vpn-current.mmdb \
            --schema examples/vpn.schema.json \
            --policy examples/release.policy.json \
            --smoke fixtures/vpn-smoke.json \
            --sample 100000 \
            --markdown report.md \
            --html report.html

      - name: Upload report
        uses: actions/upload-artifact@v4
        with:
          name: mmdb-audit-report
          path: |
            report.md
            report.html

For stricter release gates, use diff directly:

mmdbforge diff artifacts/vpn-previous.mmdb artifacts/vpn-current.mmdb \
  --sample 100000 \
  --fail-threshold changed_percent=25 \
  --fail-on-missing-field confidence \
  --fail-on-drop privacy.vpn_provider

Data Model

MMDB Forge flattens nested record fields into dotted paths:

{
  "privacy": {
    "is_vpn": true,
    "vpn_provider": "NordVPN"
  },
  "confidence": 95
}

becomes:

privacy.is_vpn
privacy.vpn_provider
confidence

This makes schema rules, diff summaries, CI checks, and smoke expectations easy to write and easy to review.

Why This Exists

When teams build their own MMDB files, failures are rarely obvious from a single lookup. Real release problems look like this:

the new database is 3x larger
some fields disappeared
country_code suddenly became registry country
confidence escaped the 0..100 range
all VPN records became risk_score=100
/32 records exploded unexpectedly
provider names disappeared
IPv6 coverage broke
known smoke-test IPs changed behavior

MMDB Forge gives those problems names, commands, and CI failure modes.

Project Layout

cmd/mmdbforge/      CLI entrypoint
internal/lookup/    inspect and explain commands
internal/diff/      sampled release diff
internal/schema/    schema validation
internal/stats/     field coverage and top values
internal/smoke/     known IP regression tests
internal/audit/     release audit orchestration
internal/report/    JSON and Markdown output
examples/           schema and smoke examples
docs/               command guides and CI notes

License

MIT. See LICENSE.

Name		Name	Last commit message	Last commit date
Latest commit History 7 Commits
cmd/mmdbforge		cmd/mmdbforge
docs		docs
examples		examples
internal		internal
LICENSE		LICENSE
README.md		README.md
go.mod		go.mod
go.sum		go.sum

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MMDB Forge

What It Does

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Quick Start

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inspect

explain

diff

explain-diff

lint cidr

validate

stats

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smoke

test

prefixes

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audit release

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MMDB Forge

What It Does

Install

Quick Start

Commands

inspect

explain

diff

explain-diff

lint cidr

validate

stats

fields

smoke

test

prefixes

bench

audit release

CI Example

Data Model

Why This Exists

Project Layout

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