Config drills
The configuration languages that run modern infrastructure — JSON, YAML, TOML, JSON Schema, Terraform HCL, and Azure Bicep — learned the only way that sticks: by writing and fixing real config. Every drill is graded live in your browseragainst the actual parsers and validators (JSON.parse, js-yaml, Ajv, and purpose-built TOML/HCL/Bicep parsers). No AI, no autocomplete — type it until it's reflex.
Why this matters:Kubernetes manifests, CI pipelines, Docker Compose, and Terraform/Bicep templates are all config. These five languages underlie the vast majority of it — and the classic traps (a quoted number, the YAML “Norway problem,” a too-loose schema, single-vs-double quotes in HCL/Bicep) are exactly what break real deployments.
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JSON
0/5 doneThe lingua franca of APIs and config — strict syntax, no comments, no trailing commas.
1. Your first JSON objectWrite a JSON object describing a service with three fields:easy2. A JSON arrayWrite a JSON array (a list) holding exactly these three port numbers, in order: 80, 443, 8080.easy3. Nested objects and arraysWrite a JSON object for a container with:medium4. Fix the broken JSONThis config is INVALID JSON — it has the three most common mistakes: a comment, single quotes, and a trailing comma. Fix it so it parses to: name = "api", retries = 3, debug = false.medium5. A database config blockWrite a JSON object with a "database" object containing host ("db.internal"), port (5432), and ssl (true), plus a "replicas" array of two host strings: "db-1" and "db-2".medium
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YAML
0/6 doneKubernetes, CI, and Compose all speak YAML — indentation is structure, and the type traps are real.
1. Your first YAMLWrite YAML with three keys:easy2. A YAML listWrite a YAML mapping with a key "ports" whose value is a list of three numbers: 80, 443, 8080. Use the block (dash) style.easy3. Nested maps by indentationWrite YAML for a container: image is nginx:1.27, and a nested "resources" map with cpu "500m" and memory "256Mi".medium4. Quote to keep it a string (type trap)YAML infers types, and that bites. Make both of these STRINGS:hard5. A multi-line block scalarWrite YAML with a key "script" whose value is a literal block (using |) containing exactly these two lines:medium6. A minimal Kubernetes PodWrite a minimal Kubernetes Pod manifest:hard
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TOML
0/8 doneThe config format behind pyproject.toml and Cargo.toml — INI-like [tables] with real types, quoted strings, and bare numbers/bools.
1. Keys and valuesWrite two top-level key/value pairs:easy2. Quote your stringsThis TOML is broken — the value is an unquoted bare word, which TOML rejects. Fix it so `env` is the string "prod".easy3. Types: quoted vs bareWrite three top-level keys with the RIGHT types:easy4. A [table]Create a `[server]` table holding two keys:medium5. Nested tables (dotted header)Write a dotted table header `[database.primary]` with:medium6. ArraysWrite a top-level key `ports` set to an array of the three NUMBERS 80, 443, and 8080.medium7. Inline tablesWrite a key `owner` set to an INLINE table on one line, holding:medium8. Array of tables [[…]]Use `[[products]]` to define a LIST of two product tables:hard
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JSON Schema
0/13 doneWrite the rules that validate config — the contract behind Kubernetes CRDs, API request validation, and IaC linting.
1. Require an object with a string fieldWrite a JSON Schema (draft-07) that describes an OBJECT with a property "name" that must be a string, and mark "name" as required.easy2. Two required fields with typesWrite a schema for an object with "name" (string) and "age" (integer), BOTH required.medium3. Constrain a number's rangeWrite a schema for an object with a required "port" that is an integer between 0 and 65535 (inclusive).medium4. An array of stringsWrite a schema for an object with a required "tags" property that is an array of strings with at least 1 item.medium5. Restrict to a set of values (enum)Write a schema for an object with a required "level" that must be exactly one of: "debug", "info", "warn", "error".hard6. Validate a nested objectWrite a schema for an object with a required "server" property that is ITSELF an object with a required "host" (string) and a required "port" (integer). Anything missing host or port inside server must be rejected.hard7. One of two shapes (oneOf)Write a schema for an object with a required "id" that may be EITHER a string OR an integer — but nothing else (no boolean, no object). Use oneOf.hard8. Match a string pattern (regex)Write a schema for an object with a required "sku" string that must match the pattern: lowercase letters, a hyphen, then digits — e.g. "web-01". Reject "Web01" and "web".hard9. Forbid unknown fields (additionalProperties)Write a strict schema: an object with a required "name" (string) and NO other properties allowed. A doc with an extra key like "extra" must be rejected.hard10. Reuse a definition with $refDefine an "address" shape ONCE and reuse it twice. Write a schema for an object with required "billing" and "shipping", where EACH is an object with a required "street" (string) and "city" (string). Put the address shape in "definitions" and point at it with "$ref": "#/definitions/address".hard11. Validate a string format (email)Write a schema for an object with a required "email" that is a string in valid EMAIL format, and an optional "website" that is a string in valid URI format. Reject a malformed email and a malformed URL.medium12. Conditional rules (if / then)Write a schema for a payment object with a required "method" that is either "card" or "cash". IF method is "card", THEN "cardNumber" (a string) must also be present. A cash payment needs no card number.hard13. Constrain every value of a free-form mapYou have a "weights" map with arbitrary keys, but EVERY value must be a number that is 0 or greater. Write a schema (for the map object itself) where any property is allowed by name, but each value must be a number ≥ 0. Reject a negative number and a string value.hard
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HCL (Terraform)
0/6 doneThe language Terraform speaks — blocks, attributes, and references that provision cloud infrastructure everywhere.
1. Your first HCL blockWrite a Terraform resource block:easy2. Attribute typesWrite these four top-level attributes with the RIGHT types (no block needed):easy3. A variable blockDeclare a Terraform input variable:medium4. Lists and mapsWrite a resource `resource "azurerm_network_security_rule" "web" { … }` with:medium5. An Azure resource group + subnet referenceWrite TWO blocks:hard6. Fix the broken HCLThis block has the two most common HCL mistakes made by people coming from JSON/YAML: it uses single quotes, and it puts a colon instead of `=`. Fix it so the resource "aws_s3_bucket" "logs" has bucket = "my-logs" and versioning = true.medium
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Bicep (Azure)
0/5 doneAzure's own infrastructure-as-code language — params, resources, and objects that deploy to Azure Resource Manager.
1. Your first Bicep paramDeclare a Bicep parameter:easy2. Variables and typesDeclare three variables with the right types:easy3. A Bicep objectDeclare a variable `settings` holding an object with:medium4. An Azure resourceDeclare an Azure resource group in Bicep:hard5. Fix the broken BicepThis Bicep came from someone who writes JSON: it uses double quotes and comma-separated fields. Fix it so `var config` is an object with name = 'api' and retries = 3.medium