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Data and structured data (10)

Where should I fix this JSON error?

An error at a closing brace may have started earlier. Repair small examples to understand error locations, strings versus numbers, and what formatting can actually establish.

Tools to use: JSON formatter

Which settings changed?

A wall of changes does not always mean many settings changed. Separate reordering from changed values, then test when ignoring array order is appropriate.

Tools to use: JSON diff

Extract only the fields you need from an API response

Need just the names from a long JSON response? Select locations with JSONPath instead of copying search matches, and learn to distinguish no matches, null, and missing fields.

Tools to use: JSONPath extractor

Turn JSON into a table with CSV

JSON converted to CSV and back no longer has the same nulls or number types. Separate successful conversion from preservation by testing the round trip.

Tools to use: JSON ⇔ CSV CSV viewer and editor JSON ⇔ YAML JSON ⇔ TOML

Check YAML that fails to load

YAML can parse successfully and still describe the wrong settings. Experiment with indentation, strings versus booleans, and multiline text before trusting a successful format.

Tools to use: YAML formatter

Find missing fields and incorrect types

JSON formats successfully, but an API rejects it. Check required fields, types, and allowed values with a small schema, while keeping the limits of validation clear.

Tools to use: JSON Schema validator

Why will this XML not parse?

Fix XML by separating mismatched tags, attributes and special characters. A small experiment also shows what successful formatting cannot validate.

Tools to use: XML formatter

Why are my CSV columns misaligned?

Commas in an address and newlines in notes can look like shifted CSV columns. Inspect quoted boundaries and compare the same values in a table and JSON.

Tools to use: CSV viewer and editor JSON ⇔ CSV

What happens to null and dates when converting JSON to TOML?

When moving JSON settings to TOML, inspect nulls, dates and comments. A successful conversion is only the start: compare types and meaning after a round trip.

Tools to use: JSON ⇔ TOML

Why did the last digits of a large JSON ID change?

If the last digit of an API ID changes, trace receiving, parsing, conversion and storage separately. Distinguish a digit string from a numeric value.

Tools to use: JSON formatter JSON diff

Text and regular expressions (8)

Why does text exceed a byte limit?

A short name exceeds a limit, but removing an emoji fixes it. Compare visible characters, UTF-16 units, and UTF-8 bytes to discover whether the form and storage count different things.

Tools to use: Text and byte counter

Find changes in text or configuration files

One intended edit produces a screenful of differences. Locate changes by line, inspect them by character, and decide when ignoring whitespace is safe.

Tools to use: Text diff

Remove duplicate lines, blank lines, and extra spaces

A pasted list contains blank lines, stray spaces, and duplicates. Change one option at a time before cleaning everything, and decide what should count as the same item.

Tools to use: Line tools

Find added and removed items between two lists

Which requested IDs are missing from the registered list? Separate common, additional, and missing items even when the two lists use different orders.

Tools to use: List set operations

Check what your regular expression actually matches

Extracting IDs from a log also captures lookalikes. Test examples that must match alongside examples that must not, then inspect extraction and replacement separately.

Tools to use: Regular expression tester

How can I standardize names across naming conventions?

Compare user_id with userId, then test acronyms, digits and naming collisions before changing an API boundary.

Tools to use: Case converter

Split a delimited list without losing empty items

Turn a comma-separated list into lines without losing empty items or meaningful spaces. Compare splitting, joining and wrappers with small examples.

Tools to use: Split and join text

Make a README easier to follow with Markdown

A README should help someone start a task. Use headings, code blocks and tables to reveal the next action rather than merely decorate the page.

Tools to use: Markdown preview

Encoding and character sets (6)

What is inside this Base64 string?

Decode an unfamiliar string, then experiment with Unicode, newlines, and Base64url. Learn why unreadable-looking text is not the same as protected information.

Tools to use: Base64 converter SHA hash calculator JWT decoder

Handle non-ASCII text, +, and %20 in URLs

Spaces become %20 or +, and C++ changes meaning. Distinguish whole URLs, individual values, and form encoding to locate the transformation.

Tools to use: URL encoder

Why do identical-looking strings compare differently?

A copied name looks identical but search cannot find it. Inspect composed forms, width variants, and invisible characters to separate normalization issues from other differences.

Tools to use: Unicode inspector Unicode normalizer

Read a garbled CSV using its character encoding

A CSV opens as garbled text. Before saving it again, establish how to decode the original bytes and distinguish a wrong interpretation from lost information.

Tools to use: Character set converter

Decode Unicode escapes and HTML entities

A log shows \u3042 and a page shows &. Distinguish escaped notation from damaged text, then decode only the intended layer.

Tools to use: Unicode escape converter HTML entity converter

What text is hidden in these UTF-8 bytes?

Decode e3 81 82 from a log, compare hex with binary and round-trip UTF-8 text to see why one character can occupy several bytes.

Tools to use: Text ⇔ bytes Unicode inspector

Date, time, and schedules (7)

What date is this 10- or 13-digit timestamp?

A log date becomes 1970 or shifts by nine hours. Change seconds versus milliseconds separately from display timezone to check whether values identify the same instant.

Tools to use: Unix time converter Time zone converter

What time is an overseas meeting in my time zone?

What time is 21:00 Tokyo in New York? Include the event date, avoid assuming a year-round offset, and distinguish skipped and repeated local times.

Tools to use: Time zone converter

Check a weekday cron schedule from 09:00 through 17:59

Does a weekday-at-nine schedule also run on the first of the month? Inspect candidates from a fixed date to uncover weekday, start-boundary, and daylight-saving assumptions.

Tools to use: Cron builder and inspector Time zone converter

Is one month after month-end the same as 30 days later?

What is one month after January 31? Compare a month, thirty days, month-end, and twenty-four hours to uncover renewal and deadline assumptions.

Tools to use: Add or subtract date/time Date and time difference

How many working days remain before a deadline?

How many business days lie between Friday and Monday? Vary weekends, custom holidays, and endpoint inclusion to explain one-day differences in schedules.

Tools to use: Business day calculator

How long is PT90M, and is P1M the same as PT1M?

Read PT90M as a duration, compare seconds and components, and distinguish calendar months from fixed elapsed time.

Tools to use: Duration converter

Why can January belong to the previous ISO week-year?

Why can January 1 belong to the previous year's week 53? Check weekly reports by converting dates and ISO week identifiers both ways.

Tools to use: ISO week number

Numbers, units, and bits (7)

Compare GB with GiB and Mbps with MB/s

Did a 1 TB drive lose capacity when it displayed about 931? Is 12.5 MB/s slow for 100 Mbps? Compare different units measuring the same quantity.

Tools to use: Data unit converter

Why can 0.1 + 0.2 differ from 0.3?

Investigate the tiny extra digits in 0.1 + 0.2 by separating number representation from rounding. Fixing the display and defining calculation rules are different tasks.

Tools to use: Decimal calculator IEEE 754 inspector

How many bits does a large ID need?

A long ID changed its last digit after copying. Investigate integer ranges, required bit width, and hexadecimal conversion rather than relying on the label '64-bit'.

Tools to use: Integer range Radix converter

From 120 ms to 90 ms: what is the percentage decrease?

120 ms to 90 ms is a 25% decrease, but returning to 120 ms is a 33.3% increase. Change the baseline to distinguish reductions, proportions, and percentage points.

Tools to use: Percentage calculator

Which flags are set in the value 13?

A setting of 13 need not mean feature number 13. Inspect binary positions and use AND, OR and XOR to test combined flags.

Tools to use: Bitwise calculator Radix converter

Why can ff mean either 255 or -1?

Explore why FF can represent 255 or −1, and keep signed interpretation, truncation and right shifts distinct.

Tools to use: Bitwise calculator Integer range

Resize an image while controlling proportions and rounding

A 16:9 image at 320 pixels wide is 180 pixels high. What about 321? Separate proportions, rounding and cropping.

Tools to use: Ratio and aspect ratio Decimal calculator

IP and network calculations (7)

What range does 192.0.2.10/24 cover?

Does 192.0.2.10/24 identify one host or a range? Change the prefix, compare boundaries and counts, and see why subtracting two is not universal for /31 and /32.

Tools to use: IPv4/CIDR calculator

Is this IP inside the specified CIDR?

Is this IP inside the allowed range? Compare a host as /32 or /128 instead of matching strings, and distinguish containment, intersection, and directional differences.

Tools to use: IP and CIDR comparison

Split a network for departments with different host counts

Split a /24 between four teams, or size blocks for different host counts. Compare equal splitting with VLSM and inspect boundaries and unallocated space, not just capacity.

Tools to use: Subnet splitter

Shorten a CIDR list without expanding its range

Shorten a long CIDR list without adding addresses. Test adjacent, duplicate, and gapped blocks to distinguish exact aggregation from covering everything with a broader range.

Tools to use: IP range ⇔ CIDR CIDR aggregation IP and CIDR comparison

Compare compressed IPv6 addresses and their ranges

Is a short IPv6 address in a log the same as a long one in configuration? Expand it, compare numeric values, and distinguish one address from a /64 range.

Tools to use: IPv6 notation converter IPv6/CIDR calculator

Is this large log integer an IP address?

A log value such as 3221225994 may encode an IP address. Convert it both ways while checking family, signedness and byte order.

Tools to use: IP integer converter

Can /31 and /32 networks be useful?

Compare /30, /31 and /32 by separating address counts from the rules for using them on a link.

Tools to use: IPv4/CIDR calculator Subnet splitter

Infrastructure estimates (8)

How long will a file transfer take?

How long does 1 GiB take at 100 Mbps? Align bits, bytes, efficiency, and GB/GiB, then estimate duration or the rate needed to meet a time budget.

Tools to use: Data transfer time

How much downtime does 99.9% availability allow?

How many minutes of downtime correspond to 99.9%? Compare 30 and 31 days, reverse the calculation, and separate time-based availability from request success rate.

Tools to use: Availability and downtime

How much space do 30 days of logs need?

How much space do thirty days of logs need? Start with event count and size, then vary compression and stored copies to see what drives capacity.

Tools to use: Log storage estimate

Estimate storage for full and incremental backups

Does keeping two generations of 100 GB require only 200 GB? Include increments and observation timing to see why an older full backup may still be needed.

Tools to use: Backup storage estimate

How much RAID capacity do four 4 TB disks provide?

Why do four 4 TB drives not always provide 16 TB? Change RAID level and spare count to separate raw capacity, redundancy, and modeled usable space.

Tools to use: RAID capacity

Why does high IOPS not guarantee fast file transfers?

IOPS alone does not determine throughput. Change the average I/O size to see how the same operation count moves different amounts of data.

Tools to use: IOPS and throughput Data unit converter

Why does a distant transfer depend on more than bandwidth?

A fast link can still struggle over long round trips. Estimate the data in flight from bandwidth and RTT without treating the result as a diagnosis.

Tools to use: Bandwidth-delay product

At 100 requests per second, how many are in flight?

At 100 arrivals per second and 0.2 seconds mean residence, the average population is 20. Distinguish this from peaks, threads and CPU requirements.

Tools to use: QPS and concurrency

Hashes, IDs, and randomness (7)

Does a downloaded file match the published hash?

Did you download the intended file? Compare SHA-256 digests, investigate newline and archive differences, and understand what a match cannot prove.

Tools to use: SHA hash calculator

Inspect JWT contents and expiration claims

An expired token immediately after login? Read exp, nbf and iat as UTC times, compare the clock, and distinguish decoding from signature verification.

Tools to use: JWT decoder

Debug the inputs to a webhook HMAC signature

A webhook signature does not match: before changing the key, check a known example, body newlines, JSON whitespace, key encoding and output representation.

Tools to use: HMAC calculator

Generate test IDs and random strings

Should test IDs, secret tokens and repeatable fixtures use the same randomness? Try UUID v4/v7 and random tokens, then choose according to their role.

Tools to use: UUID generator Random token generator Password generator

Does a matching CRC prove a file is safe?

Matching CRC32 is not proof of safety. Use a known input to check the variant, then distinguish corruption detection from authenticating a source.

Tools to use: CRC32 checksum SHA hash calculator

How long should a random ID be?

Eight characters are not a complete specification. Compare alphabet, length and generated count, and distinguish collisions from resistance to guessing.

Tools to use: Entropy and collision probability Random token generator

Does a UUID contain a timestamp? Compare v4 and v7

UUID v4 and v7 have the same length but different structure. Explore generation and timestamp inspection without treating order as authenticity.

Tools to use: UUID generator

Web, UI, and CSS (7)

Check text contrast in light and dark themes

Is that pale gray helper text readable? Compare white backgrounds, translucent text and dark themes, then decide what to adjust first.

Tools to use: Color converter Contrast ratio

How many rem is 16 px at different base sizes?

How many rem is 24px? Explore root-font assumptions, nested em and viewport-dependent vw before transferring design dimensions into CSS.

Tools to use: CSS unit converter

Arrange equally spaced cards with Flexbox and Grid

Three cards refuse to line up: Grid or Flexbox? Change columns, gaps, wrapping and long content one at a time to find the cause.

Tools to use: Flexbox and Grid generator

Review a URL before creating a QR code

Before printing a QR code, inspect its domain, repeated query parameters, quiet zone and decoded text to avoid rework.

Tools to use: URL parser QR code generator

Why are my gradient colors in the wrong place?

The colors are right but the transition is in the wrong place. Start with angle and order, then read the stop positions in generated CSS.

Tools to use: CSS gradient generator

Why does my card shadow look blurry?

A larger shadow can make a card look blurry rather than raised. Adjust offset, blur, spread and opacity separately.

Tools to use: Box shadow generator

Why can black text have poor contrast when transparent?

The same text color changes with alpha and the surface behind it. Check contrast using the composited foreground and background.

Tools to use: Contrast ratio Color converter

SQL and test data (7)

Make long SQL conditions and joins easier to read

Turn a one-line SQL statement into something you can inspect: selected fields, filters, parentheses, joins and parameter mapping.

Tools to use: SQL formatter

Turn a list of IDs or names into an SQL IN clause

Before turning a list into SQL, check leading zeros, quotes, duplicates and NULL. Distinguish preparing an IN clause from safe application parameter handling.

Tools to use: SQL IN clause generator

Create INSERT statements from sample CSV or JSON

What happens to empty strings, NULL and missing fields when JSON or CSV becomes INSERT? Inspect a small fictional dataset before considering database use.

Tools to use: JSON/CSV → INSERT

Generate repeatable test data without real records

Reproduce 'it broke with the previous data' by fixing a seed and schema. Generate fictional rows, change formats, and add boundary cases randomness alone may miss.

Tools to use: Mock data generator