Learn what your code does.

rngo is a dynamic code analyzer that simulates usage, records everything and surfaces patterns

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$ rngo eval

Simulation
time: 2026-11-12 13:10:10
auth-api:        18342 inputs, 18342 outputs
auth-postgres:   9120 inputs, 0 outputs
inventory-api:   25610 inputs, 25610 outputs
inventory-mysql: 14288 inputs, 0 outputs
order-api:       12907 inputs, 12907 outputs
order-dynamo:    12907 inputs, 0 outputs
logs:            0 inputs, 412880 outputs

Audit
auth-unique-emails: 0 (passed)
auth-no-server-errors: 0 (passed)
auth-session-expiry-enforced: 0 (passed)
inventory-no-negative-stock: 0 (passed)
inventory-sku-unique: 0 (passed)
inventory-no-server-errors: 0 (passed)
order-total-matches-items: 0 (passed)
order-no-duplicate-charges: 2 (failed)
order-no-server-errors: 0 (passed)
order-reserves-inventory: 0 (passed)
logs-minimal-errors: 31 (failed)

9 passed, 2 failed

Meet the rngo spec

A declarative description of a system's behavior, in terms of a channels, effects and signals. The channels and effects model realistic usage while the signals set expectations for observed behavior.

Channels

A channel specifies how to send formatted inputs to and receive outputs from an interface in your system.

Read about channels →

spec.yml

channels:
  db:
    type: stream
    command: sqlite3 db.sqlite
    format:
      type: sql
  api:
    type: exec
    format:
      type: template
      template: >-
        curl -sS -X {{data.method}}
        "${API_BASE_URL:-http://localhost:5173}{{{data.path}}}"
        {{#if data.body}}
        -H 'Content-Type: application/json'
        --data '{{json data.body}}'
        {{/if}}

Effects

An effect defines a stream of inputs, which are randomly-generated JSON values with logical (possibly backdated) timestamps.

Read about effects →

spec.yml

effects:
  users.create:
    trigger: hz(100, day)
    start: now - years(2)
    channel: db
    metadata:
      table: USERS
    generator:
      type: object
      properties:
        id:
          type: number
          minimum: 1
          scale: 0
          step: 1
        name:
          type: string
          pattern: .{2,64}
        email:
          type: function
          expression: "'user' + number + '@example.com'"
          variables:
            number:
              type: number
              minimum: 10000
              maximum: 99999
              scale: 0
  articles.post:
    # …

Signals

A signal is a SQL query over every channel's inputs and outputs, along with an expected result.

Read about signals →

spec.yml

signals:
  api-minimum-title-length:
    type: sql
    query: >
      SELECT count(*)
      FROM outputs o
        JOIN inputs i ON o.input_id = i.id
      WHERE i.effect = 'articles.post'
      AND length(i.data ->> '$.title') < 10
      AND o.data NOT LIKE '%422 Unprocessable Content%';
    expect: result == 0
  api-no-server-errors:
    type: sql
    query: >
      SELECT count(*) FROM outputs
      WHERE channel = 'api' AND data LIKE '%500%';
    expect: result == 0
  log-minimal-errors:
    type: sql
    query: >
      SELECT count(*) FROM outputs
      WHERE channel = 'log' AND data LIKE 'ERROR%';
    expect: result < 20