Developer & Tech Utilities
187 tools
Quick placeholder and sample values for development, testing and documentation — hostnames, slugs, filenames, status codes and more. Every value is clearly a random example, never a real credential, address or in-use identifier.
Showing 187 of 187 tools.
QA, errors & workflow
- Date Edge Case GeneratorThe dates that break software — leap days, month ends, clock changes, ISO week boundaries — as real test data.
- Test Matrix GeneratorTurn parameters and their values into a test matrix — full factorial, a random sample, or all-pairs coverage in a fraction of the cases.
- API Failure Scenario GeneratorNine distinct ways an API call fails, each saying where in the request it broke, whether a retry is safe, and what the client should do.
- Pagination Test Case GeneratorWork out every page boundary for a list, and the specific totals where pagination bugs actually live.
- State Transition Path GeneratorDescribe a state machine and walk random valid paths through it, to find the routes your tests are not covering.
- Correlated Dataset GeneratorTwo numeric columns with a correlation you choose, plus optional blanks, duplicate rows and outliers — for testing charts, cleaning pipelines and statistics teaching.
- Rate Limit Scenario GeneratorThe ways rate limiting actually bites — missing Retry-After, per-key budgets, silent throttling — with the expected client behaviour for each.
- Cache Scenario GeneratorThe ways a cache serves a wrong answer quickly — stale reads, herds on expiry, cached negatives, keys that collide across tenants.
- Idempotency Scenario GeneratorThe cases an idempotency key has to survive — same key with a different body, two retries in flight at once, keys that expire before the client gives up.
- Feature Rollout Cohort GeneratorWorks out who is in a staged rollout and which variant they see, so that widening it never takes the feature off anybody.
- System Reliability CalculatorWhat a system's availability really is once the parts are in a chain, doubled up, or needed some-of-many.
- Complexity Comparison GeneratorTwo algorithms compared at every input size, with the crossover where better growth finally beats a large constant.
- Permission Matrix GeneratorEvery role, resource and action combination laid out as a checklist, with the denials listed because those are the ones worth testing.
- Input Validation Scenario GeneratorLength-rule test cases sitting exactly on each boundary and either side, plus the whitespace cases people forget.
- Topological Sort Challenge GeneratorDependency sets with a valid order and a count of how many valid orders exist in total.
- Binary Search Scenario GeneratorSorted lists with the full binary search trace, every step's range shown, and the logarithmic bound as the check.
- Access Control Scenario GeneratorPairwise test cases across authentication, role, resource state and origin, with every pair of values proved covered.
- Token Lifetime Scenario GeneratorBoundary test cases for session and token expiry, including the clock-skew window that trips most implementations.
- Cron Schedule CalculatorReads a cron expression and lists the next runs, including the day-of-month and day-of-week rule people misread.
- htaccess Redirect GeneratorSample RewriteRule redirects, each applied to an example path to show where it actually lands.
- Sorting Network GeneratorBuilds a fixed sequence of compare-and-swap steps that sorts any input, verified against every possible sequence of zeroes and ones.
- Assembly Line Balancing GeneratorAssigns tasks with precedence rules to workstations under a fixed cycle time, and says how many stations the work alone would have needed.
- Interval Scheduling GeneratorPicks the largest possible set of non-overlapping bookings, and shows how many the obvious first-come rule would have lost.
- Job Sequencing With Deadlines GeneratorChooses which deadline-bound jobs to run, on one machine or several in parallel, for the highest total profit — proved against exhaustive search.
- DFA Minimisation GeneratorGenerates a finite automaton, merges the states no string can tell apart, and runs both machines over every short string to prove the language is unchanged.
- Timezone Edge Case GeneratorThe moments that break time handling — the hour that never happens, the hour that happens twice, offsets that are not whole hours — as test data you can commit.
- Edge Case Prompt GeneratorA 'what happens if…' testing prompt to jog which edge case to check next.
- Exception Message GeneratorA fictional exception message for a mockup, log sample or error-handling test, not tied to any real library.
- Boundary Value GeneratorA standard numeric or string boundary value used in software testing, like a max-int or an empty string.
- Log Entry GeneratorA sample structured log line with timestamp, level and service name, for testing a log viewer.
- User Story GeneratorAn 'As a…, I want…, so that…' user story, distinct from the site's acceptance-criteria prompt tool.
- Issue Title GeneratorA realistic example software-issue title, for demos or teaching.
- Error Code Sample GeneratorA plausible error code and description pair for mockups, tutorials or test fixtures.
- Bug Report Prompt GeneratorA prompt to check your bug report actually includes, so it's reproducible on the first read.
- Pull Request Title GeneratorA conventional-commit-style pull request title, distinct from the site's commit-message prompt tool.
- Release Note Prompt GeneratorA prompt to check your release note actually covers, distinct from a bug-report or PR-title tool.
- Test Case Name GeneratorA 'should X when Y' test-case description, distinct from the site's test-suite name tool.
- Test Suite Name GeneratorA realistic test-suite/describe-block name, distinct from an individual test-case name.
API & network testing
- Subnet CalculatorWhat a CIDR block actually contains, how it divides without leaving a gap, and the two prefixes where 'subtract two' is wrong.
- Retry Backoff Schedule GeneratorWork out what a retry policy actually does — every delay, the running total, and where a cap or jitter changes it.
- JWT DecoderReads the header and claims out of a JSON Web Token, explains the standard ones, and never pretends to have checked the signature.
- Distributed Trace GeneratorBuilds a sample request trace — one call, everything it called, and when — with every call sitting inside the one that made it.
- cURL Command GeneratorA sample curl request with headers and a JSON body, quoted properly and checked by reading it back as a shell would.
- Great Circle Route GeneratorThe shortest path between two points on the globe, with waypoints along it and the constant-bearing route shown for comparison.
- Consistent Hashing Ring GeneratorDistributes keys around a hash ring and measures exactly how many move when a node joins, with every move checked to go to the new node.
- Map Projection Distortion CalculatorShows exactly how much a projection stretches the map at each latitude, with every figure recomputed from the secant of the latitude.
- HTTP Status Code GeneratorA real HTTP status code with its standard meaning.
- Mock API Error GeneratorA sample JSON error response, distinct from the site's success-shaped mock API response tool.
- Mock API Response GeneratorA sample successful JSON API response, distinct from the site's error-shaped mock response tool.
- Cron Expression GeneratorA cron expression built field by field, with the plain-English sentence that matches it.
- HTTP Header GeneratorA real HTTP header name with an illustrative example value, for API testing or documentation.
- SQL Query Sample GeneratorA realistic example SQL query, for teaching or documentation.
- API Endpoint Name GeneratorGenerate an example REST API endpoint path, like /api/v1/orders/{id}.
- GraphQL Query Sample GeneratorA realistic example GraphQL query or mutation, for teaching or documentation.
- Random HTTP Method GeneratorA real HTTP request method with its standard meaning.
- URL Query String GeneratorA sample URL query string with realistic parameter names, distinct from the site's URL-slug tool.
- URL Path GeneratorA random multi-segment URL path, for documentation or mockups.
- Webhook Payload Example GeneratorA fictional webhook JSON payload, for documentation or mockups.
- API Rate Limit Example GeneratorA realistic example API rate-limit response or header set.
Data formats & samples
- ISO Week Date ConverterConverts a date to its ISO 8601 week date, and shows when the ISO year is not the calendar year.
- Timestamp Sequence GeneratorGenerate an ordered run of timestamps at a set interval, with optional jitter, in ISO, epoch, SQL or date-only format.
- Test Event Log GeneratorGenerate realistic log rows in your own event vocabulary — ordered timestamps, event names, actors and status codes — as CSV, with every value you list guaranteed to appear if you ask.
- Regex String GeneratorType a regular expression and get strings that match it — parsed, generated backwards, and every one tested against the pattern by the browser's own engine.
- Random Graph GeneratorRandom graphs at a density you choose, drawn and exported as an edge list or DOT, with connectivity measured rather than assumed.
- Regression Dataset GeneratorData built from a slope and intercept you choose, with the line fitted back out of it so you can see how close estimation gets.
- Clustered Dataset GeneratorPoints grouped around known centres with the true group recorded, so you can check what a clustering algorithm actually recovered.
- Imbalanced Dataset GeneratorA classification dataset with a rare positive class, and the majority-class baseline that shows why accuracy is the wrong measure.
- Seasonal Time Series GeneratorA series built from a trend and a season you specify, with each point's parts recorded so a decomposition can be checked rather than trusted.
- Calendar File (.ics) GeneratorWrites a proper .ics calendar file for one event or a whole schedule — repeats, reminders, all-day dates and awkward punctuation included — and reads it back to prove it survived.
- DAG GeneratorDirected acyclic graphs where the absence of cycles is structural rather than checked afterwards — for testing schedulers, build systems and topological sorts.
- Random Tree GeneratorRandom trees with exactly one path between any two nodes — n nodes, n minus 1 edges, no cycles, guaranteed connected.
- Network Topology GeneratorStar, ring, mesh, line and hub-and-spoke topologies drawn to scale, with the edge count each shape forces.
- JSON Formatter and ValidatorTidies or minifies JSON, says exactly where an invalid document goes wrong, and proves the data still says the same thing.
- Lorem Ipsum GeneratorPlaceholder text in nine registers, by the word, sentence or paragraph — and exactly the number you asked for, counted back off the result.
- Relational Test Data GeneratorBuilds three linked tables of sample rows where every key joins up — plus, if you want them, an exact number of ones that do not.
- List CleanerRemoves duplicates, sorts and counts a pasted list, with every line traced back to the one you pasted.
- Synthetic Test Data GeneratorBuild a whole table of fictional records from the fields you choose, then export them as a table, JSON, CSV or SQL inserts.
- Floating Point Pitfall GeneratorWorked examples of the four ways decimal arithmetic goes wrong on a computer, each shown with the values actually stored.
- Markdown Table GeneratorTurns pasted rows into a tidy Markdown, HTML, plain-text or CSV table, and reads the result back to prove nothing was mangled.
- Sorting Algorithm Trace GeneratorAn array, an algorithm, and the state after every pass, with the comparison and move counts that distinguish the three.
- Docker Compose File GeneratorA sample docker-compose.yml with an app service, a data store, a volume and a network — parsed back and checked before you see it.
- Binary Search Tree GeneratorAn insertion order and the tree it builds, with all three traversals, the height, and whether it came out balanced.
- Hash Table Scenario GeneratorKeys distributed into buckets by modulo hashing, with collisions, chain lengths and empty buckets all recounted from the table.
- Logistic Regression Dataset GeneratorTwo-feature classification data with a known decision boundary, and the majority-class baseline any model must beat.
- Kubernetes Manifest GeneratorA sample Deployment, Service or ConfigMap with the required keys present, the names legal and the labels actually matching.
- Logic Gate Circuit GeneratorRandom acyclic gate circuits with their equivalent expression and full input-output table, the two required to agree everywhere.
- Binary Heap GeneratorMin or max heaps built one insertion at a time, shown level by level, and drained to prove they sort.
- Outlier Dataset GeneratorContaminated samples where the planted outliers are labelled, so a detection rule can be scored on both kinds of error.
- Missing Data GeneratorDatasets with gaps under all three mechanisms — completely at random, dependent on a column you can see, and dependent on the missing value itself.
- Text Diff GeneratorCompares two texts line by line and shows the smallest set of changes, checked by applying them back to the original.
- package.json GeneratorA sample package.json with a legal name, a real semantic version, plausible scripts and dependency ranges npm would accept.
- Letter Frequency AnalyserLetter counts against English norms, with the index of coincidence that tells natural language apart from random text.
- Circuit Load CalculatorWhat a set of equipment draws against a breaker rating, with the eighty per cent rule a sustained load should respect.
- SAT Instance GeneratorRandom 3-SAT instances in conjunctive normal form, labelled satisfiable or not by exhaustive search, with a satisfying assignment when one exists.
- Trie GeneratorPrefix trees over words chosen to overlap, with the storage saving measured and the contents checked in both directions.
- Sparse Matrix GeneratorMatrices with most cells zero, in both dense and compressed-sparse-row form, with the storage comparison stated honestly in both directions.
- Correlation Matrix GeneratorCorrelation matrices built from a factor model, so they are positive semi-definite — which hand-picked numbers usually are not.
- Gray Code GeneratorBit sequences where consecutive entries differ in exactly one position, checked at every step including the wrap.
- Balanced Bracket GeneratorEvery balanced bracket sequence of a given size, counted against the Catalan numbers and each checked by the running-depth rule.
- Burrows-Wheeler Transform ToolThe Burrows-Wheeler transform of your text with every sorted rotation shown, checked by decoding it back to the original exactly.
- LZ77 Compression ToolLZ77 tokens for your text with a window size you choose, decoded back and compared against the original before display.
- Quadtree GeneratorA region subdivided around clustered points, with the cells confirmed to tile it exactly and hold every point once.
- Ladder Angle CalculatorWorks out a ladder's angle and reach from its length and how far the foot sits out, against the four-to-one rule.
- Edit Distance CalculatorThe fewest single-character edits that turn one word into another, listed step by step and proved by replaying them.
- Huffman Code GeneratorBuilds an optimal prefix code for your text, shows every character's bit pattern, and decodes the bits back to prove it works.
- Hamming Code GeneratorEncodes four bits as seven, flips one on purpose, and shows the syndrome pointing straight at the corrupted position.
- Secret Sharing GeneratorSplits a number into shares where any threshold of them rebuilds it — checked by trying every combination — and fewer reveal nothing.
- Bloom Filter GeneratorFills a Bloom filter and measures its real false-positive rate against the predicted one, with every inserted item proved still present.
- Soundex Phonetic Code GeneratorSoundex codes for your own list of names, grouped by the code they share, and the pairs the algorithm can never match however alike they sound.
- Hash Avalanche DemonstratorFlips one bit of your text at a time and measures how many of the 32 hash bits change — the avalanche property, measured rather than asserted.
- Run-Length Encoding GeneratorEncodes text as runs of repeated characters, decodes it back to prove it is exact, and says plainly when the result is longer.
- Text Wrapping and Raggedness GeneratorWraps text to a fixed width greedily, scores how ragged the right edge is, and checks every word survived in order.
- Diffie-Hellman Exchange GeneratorWalks through a key exchange with numbers small enough to check by hand, confirming both sides reach the same value without sending a secret.
- Toy RSA Key GeneratorBuilds a tiny RSA key from two small primes and checks that every message in the modulus survives being encrypted and decrypted.
- One-Time Pad GeneratorEncrypts a message with a pad exactly as long as it, then removes the pad again and checks the plaintext came back letter for letter.
- Regex Pattern Sample GeneratorA common validation regex paired with a real string it matches, for testing or learning pattern syntax.
- JSON Sample GeneratorGenerate a small sample JSON object with randomised placeholder values, for API mockups.
- YAML Sample GeneratorA small sample YAML fixture, distinct from the site's JSON-sample tool.
- CSV Test Dataset GeneratorA small fictional CSV sample, including one deliberately messy row, for exercising a parser.
- Nested JSON GeneratorA small sample JSON object with one level of nesting.
- JSON Array GeneratorA small array of sample JSON objects.
- XML Sample GeneratorA realistic example XML snippet, for teaching or documentation.
- TSV Sample GeneratorA realistic tab-separated-values sample, for teaching or documentation.
Identifiers & random values
- Country Code Challenge GeneratorPractise ISO 3166-1 alpha-2 codes both ways — code to country and country to code, with the awkward ones included.
- QR Code GeneratorTurns text or a link into a QR code, then reads the finished grid back the way a scanner does to prove it works.
- Wi-Fi QR Code GeneratorA QR code that joins a phone to your network, with passwords containing semicolons and quotes handled properly.
- Contact Card QR Code GeneratorA QR code that adds you to somebody's contacts, with commas and semicolons in company names handled properly.
- Checksum and Hash CalculatorWorks out SHA-256, CRC-32, Adler-32 or FNV-1a for any text, checked against the published values.
- Check Digit Identifier GeneratorTest-data identifiers that pass their own check — IBAN, VIN, IMEI, EAN, UPC, routing and VAT numbers — each with the arithmetic that produced its check digit written out.
- EAN-13 Barcode GeneratorDraws a real EAN-13 barcode from a number, then reads the bars back the way a scanner would to prove it works.
- UUID InspectorSays which version and variant a UUID is, and pulls the timestamp out of the ones that carry one.
- De Bruijn Sequence GeneratorOne sequence containing every possible run of a given length exactly once — 10,003 keypresses for all 10,000 four-digit codes.
- Damm Check Digit GeneratorAdds a check digit that catches every single mistyped digit and every swap of two neighbours, and proves it by trying them all.
- Crypto Wallet Address GeneratorStructurally valid Bitcoin addresses for testing — Base58Check or Bech32, testnet by default, with no key behind any of them.
- Resistor Colour Code CalculatorTurns a resistance into its colour bands and reads them straight back, with the nearest value actually manufactured shown alongside.
- ULID GeneratorA correctly-shaped ULID example, for placeholder database identifiers.
- UUID Batch GeneratorFive fresh UUIDs at once, one per line.
- Random Port Number GeneratorA port number in the common ephemeral/user-registrable range.
- Semantic Version GeneratorA semantic-version-shaped string (MAJOR.MINOR.PATCH).
- Nanoid-Style Test ID GeneratorA correctly-shaped, URL-safe 21-character test ID in the nanoid visual style.
- Random Alphanumeric String GeneratorA random string of letters and digits only, no symbols.
- Ticket ID GeneratorGenerate a fictional issue-tracker-style ticket ID example, like PROJ-4821.
- Build Number GeneratorGenerate a fictional build-number example, like build-2026.09.01-a3f1.
- Invoice Reference GeneratorA plausible reference code for mockup invoices, clearly not a real transaction ID.
- Random ASCII Test String GeneratorA random printable-ASCII test string, including symbols.
- Random Unicode Test String GeneratorA random test string mixing several real Unicode blocks, including emoji.
Code & naming conventions
- Text Encoder and DecoderEncodes text as Base64, percent-encoding, HTML entities, hex or binary, and back again — accents and emoji included.
- Regular Expression TesterRuns a pattern against your text, highlights every match with its position and groups, and refuses patterns that could hang the page.
- Morse Code TranslatorTurns text into morse and morse back into text, with anything the code cannot carry listed rather than dropped.
- Text Case ConverterRewrites text as camelCase, snake_case, kebab-case and five others at once, splitting names the way a person would.
- Number Base ConverterConverts a number between binary, octal, decimal, hexadecimal and base 36, showing all five at once.
- Phonetic Alphabet TranslatorSpells anything out in the NATO phonetic alphabet, so a reference or a postcode can be read aloud without being misheard.
- Braille TranscriberTranscribes text into uncontracted braille cells and back, with the number sign handled where digits appear.
- Turing Machine SimulatorA binary increment machine run step by step, with the finished tape checked as a number: the output must be the input plus one.
- Perfect Hash GeneratorFinds a hash that sends a fixed list of keys to distinct slots, with no collisions at all.
- Semver Range ResolverSays which versions a range admits and why each of the others was rejected, including the prerelease rule.
- Git Branch Name GeneratorGenerate an example Git branch name in the common type/description format, like feature/add-login-form.
- URL Slug GeneratorA kebab-case URL slug for test data or mockups.
- Random Filename GeneratorA placeholder filename with a common extension.
- Commit Message Prompt GeneratorAn example conventional-commit-style message, for practising commit conventions.
- Environment Variable Name GeneratorGenerate an example environment-variable name in UPPER_SNAKE_CASE, like API_SECRET.
- Docker Image Tag GeneratorAn example Docker image tag, for documentation or config mockups.
- CSS Class Name GeneratorGenerate an example CSS class name in a common BEM-ish convention, like card__title.
- Database Table Name GeneratorGenerate an example database table name in common snake_case_plural convention, like app_orders.
- Feature Flag Name GeneratorA plausible feature-flag identifier for documentation, mockups or example config.
- Configuration Key GeneratorA realistic dot- or underscore-separated configuration key name, for testing config-loading code.
- Database Index Name GeneratorA realistic database index name, distinct from the site's table-name generator.
- Migration Name GeneratorA timestamped database-migration filename, distinct from the site's build-number tool.
- CSS Variable Name GeneratorA random kebab-case CSS custom-property name.
Dates & durations
Coordinates & geometry
- Cut List OptimiserWorks out how many stock lengths you need and which pieces come off each, counting the saw kerf that usually gets forgotten.
- Sheet Cut OptimiserLays your panels out on full sheets, shows where each one sits, and checks that no two overlap.
- Plus Code ConverterTurns a latitude and longitude into an Open Location Code, and shows exactly which patch of ground it names.
- Geohash ConverterTurns coordinates into a geohash, whose useful trick is that nearby places usually share a prefix.
Placeholder & test contact data
- Licence Plate GeneratorInvented plates in nine real national formats, each checked against that country's pattern and its letter set.
- Placeholder Email GeneratorGenerate a placeholder email address on a reserved example domain — never a real, deliverable address.
- Placeholder Phone Number GeneratorPlaceholder phone numbers for six countries, every one drawn from a range the country's own regulator reserves for fiction — never a real, dialable number.
- Test Address GeneratorStreet addresses for form and mock-up testing, with no postcode and no country — which is what stops them being deliverable.
- Placeholder Hostname GeneratorGenerate a placeholder hostname on the reserved example.com domain — never a real, resolvable host.
- Random IPv6 Address GeneratorAn IPv6 address for placeholder config or test data.
- Timezone Test Value GeneratorA real IANA timezone identifier for testing date/time handling across regions.
- Locale Code PickerA real BCP 47 locale code, like en-GB or ja-JP, for testing internationalisation.
- User-Agent Example GeneratorGet an illustrative example User-Agent string in the standard format, for testing — not from any real visitor.
- Department Name GeneratorA plausible internal team or department name for mockups and sample org charts.
- Language Code PickerA real ISO 639 language code alone, distinct from the site's language-plus-region locale picker.
- MIME Type PickerA random common MIME type string.
Choosing the right dev utilities tool
Tools for the moments in development where you need plausible data rather than real data: seeding a database, filling a prototype, exercising an importer, writing a fixture, or deciding which configurations to test at all. Several of these offer a seed, which swaps the cryptographic source for a deterministic one so a fixture can be committed and reproduced — reproducibility, never security. Everything is generated in your browser from deliberately fictional value banks — reserved email domains, telephone ranges regulators keep for drama, non-deliverable addresses — so nothing produced here can be mistaken for a real personal record.
- Synthetic Test Data Generator
- You need many records with fields you choose, and CSV, JSON or SQL output. It is the only tool here that takes a schema as input.
- CSV and JSON sample generators
- You need one small fixed-shape example to paste into a test or a document, not a dataset.
- UUID and identifier tools
- You need real, usable identifiers rather than examples — these produce genuine version 4 UUIDs from cryptographic randomness.
- Placeholder contact data
- You need a single fake email, phone number or address to fill a form field during testing.
- Test Matrix Generator
- The question is which combinations to test rather than what data to put in them. Pairwise coverage typically cuts a full sweep by an order of magnitude, and the coverage achieved is measured rather than claimed.
- Timestamp Sequence Generator
- You need times in order at a controlled interval, rather than the scattered independent values the random timestamp generator produces.
- Test Event Log Generator
- You want log-shaped rows — timestamp, event, actor, status — to fill a dashboard or exercise a log viewer.
- Retry Backoff Schedule Generator
- The question is what a retry policy actually does. Six exponential retries take longer than most people expect, and the table shows exactly how long.
- State Transition Path Generator
- You want journeys rather than configurations — the sequences through a workflow that nobody thought to test.
- Pagination Test Case Generator
- You need the specific totals where pagination breaks: exact divisions, partial last pages and requests past the end.
Every tool in this category draws its results in your browser. How Generate Random works explains how the randomness is produced and what happens to anything you type in.