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The Ultimate Developer Stack

Lightweight, browser-based tools for developers. No signup, no upload, no tracking.

Popular tools

Start with the tools people reach for most often in day-to-day debugging workflows.

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Media

Danmaku(XML) to ASS Converter

High-performance XML to ASS subtitle converter. Transform Bilibili/AcFun danmaku into high-quality, collision-free subtitles for Potplayer, IINA, VLC, and Movist.

Language

Japanese Character Limit Checker

Check whether Japanese text is under, over, or exactly on a target character limit such as 200, 400, 600, or 800 characters.

Language

Japanese Full/Half-width Converter (Zenkaku/Hankaku)

The definitive tool to convert Japanese text for bank forms. Instantly switch between Zenkaku (Full-width) and Hankaku (Half-width) Katakana, numbers, and symbols.

Language

Japanese Manuscript Paper Calculator

Convert Japanese text into 200-cell or 400-cell manuscript-paper length and estimate how many genkouyoushi sheets a draft will require.

Language

Japanese Reading Time Calculator

Estimate silent reading time and read-aloud duration from Japanese character count for scripts, speeches, lessons, and study materials.

Language

Japanese Text Counter - Ninja Character Counter

A specialized character counter designed for Japanese text. Instantly analyze Hiragana, Katakana, Kanji distributions, and total character limits.

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Category clusters

Explore the platform by problem space

Start from a topic area, then branch into the right tools and guides for that workflow.

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Data

JSON, CSV, SQL, timestamps, and other structured data tools for debugging, transforming, and validating payloads.

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21 tools9 guides

Language

Language-specific utilities, starting with Japanese-focused text and grammar helpers.

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11 tools6 guides

Media

Image, color, subtitle, and visual asset tools for frontend and content workflows.

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9 tools2 guides

Security

JWT, UUID, password, token, and hashing tools for auth and identity workflows.

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4 tools3 guides

Text

Regex, markdown, diff, and text analysis tools for writing, comparing, and cleaning developer-facing content.

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4 tools1 guides

Web

Tools for URLs, encodings, headers, requests, and browser-facing payload workflows.

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11 tools11 guides

Featured guides

High-signal guides that connect multiple tools into practical developer workflows.

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Language

Check Japanese Character Limits Before Submitting Essays and Entry Sheets

A practical workflow for checking Japanese character limits before submission so a draft does not fail because it is visibly short, quietly over, or counted under the wrong rule.

7 min read
Data

Data Tools Hub: JSON, CSV, SQL, Timestamps, and Developer Payload Workflows

A hub guide to choosing the right data tool for JSON, CSV, SQL, timestamps, cron expressions, and structured debugging workflows.

8 min read
Data

How to Debug REST API Responses

A practical guide to reading, validating, and decoding API responses - JSON formatting, Base64 decoding, URL decoding, and timestamp conversion.

6 min read
Media

Fansub Subtitle Workflow Hub: Danmaku, ASS, SRT, WebVTT

A practical workflow guide for fansub and anime subtitle pipelines: convert Bilibili danmaku to ASS, swap between ASS/SRT/WebVTT, and re-sync timing for different frame rates.

6 min read
Language

Japanese Writing & Content Creation Hub: Counters, Readability, and Romanization

A workflow hub for Japanese writers, teachers, and content creators — character counters, kanji density, JLPT level checking, romanization, manuscript paper, and reading-time estimation in one map.

7 min read
Language

Complete Guide to Japanese Zenkaku & Hankaku for Banking and Registration

Why do Japanese banks still require half-width Katakana? Learn the history of Zenkaku/Hankaku and how to correctly format your name for Japanese forms.

5 min read

Latest tools

Recently added tools that are already part of the current architecture and topic graph.

DataNew

Zengin Bank File Format Validator

Audit fixed-width Zengin (.txt) files for field length violations, invalid Zenkaku characters in Hankaku fields, and trailer hash total mismatches.

LanguageNew

Japanese Invoice Registration Number Validator

Batch-validate Japanese qualified invoice registration numbers (T-numbers) for the 2023 Invoice System. Checks syntax, digit count, and mod-11 checksum locally.

MediaNew

Subtitle Readability & Compliance Auditor

Validate subtitle files for character-per-second (CPS) limits, line length, and timing overlaps to ensure readability.

LanguageNew

Japanese Bank Account Batch Formatter

Batch-prepare Japanese bank transfer rows for Zengin upload — bank lookup, half-width katakana, fixed-width export.

LanguageNew

JLPT Kanji Level Checker

Paste Japanese text to see which kanji belong to JLPT N5, N4, N3, N2, or N1+. Useful for learners checking material difficulty and authors targeting a specific JLPT level.

LanguageNew

Kana ↔ Romaji Converter

Convert between hiragana, katakana, and Hepburn romaji. Handles sokuon (っ), long vowels (ー), small ya/yu/yo combinations, and ん before vowels.

LanguageNew

Kanji Density Analyzer

Measure the ratio of kanji, hiragana, katakana, and romaji in a Japanese passage. Use the kanji percentage to gauge reading difficulty for textbooks, blogs, JLPT prep, and editorial content.

MediaNew

ASS to SRT Subtitle Converter

Convert between Advanced SubStation Alpha (.ass) and SubRip (.srt) subtitle files entirely in your browser. Strips styling tags, preserves timing, handles multi-line cues.

Workflow clusters

Grouped entry points for debugging, conversion, auth, and browser-side troubleshooting workflows.

Language

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Language-specific utilities such as Japanese writing and conjugation tools.

Check Japanese Character Limits Before Submitting Essays and Entry Sheets
A practical workflow for checking Japanese character limits before submission so a draft does not fail because it is visibly short, quietly over, or counted under the wrong rule.
Estimate Japanese Reading Time for Scripts, Lessons, and Study Content
A workflow for estimating Japanese silent reading and read-aloud time so scripts, lessons, and study materials fit their real timing constraints.
Complete Guide to Japanese Zenkaku & Hankaku for Banking and Registration
Why do Japanese banks still require half-width Katakana? Learn the history of Zenkaku/Hankaku and how to correctly format your name for Japanese forms.

Data

Explore hub

Format, validate, convert, and inspect structured developer data.

How to Debug REST API Responses
A practical guide to reading, validating, and decoding API responses - JSON formatting, Base64 decoding, URL decoding, and timestamp conversion.
Check IPv4 CIDR Boundaries Before You Touch Firewall Rules
A practical workflow for checking subnet boundaries, broadcast scope, and usable host ranges before a firewall or allowlist change widens the wrong network.
JSON Formatter vs JSON Validator: Which Tool Should You Use First?
A practical comparison of JSON formatters and validators, including when to beautify, when to validate, and how to combine both in one debugging workflow.

Web

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Work with URLs, Base64, JavaScript payloads, and browser-safe encodings.

400 vs 401 vs 403 vs 422: A Practical API Error Triage Workflow
A concrete debugging workflow for separating malformed requests, authentication failures, permission issues, and validation errors before your team fixes the wrong thing.
Nested Redirect URL Debugging Checklist: Duplicate Params, Empty Trackers, and Decode Boundaries
A practical workflow for debugging redirect URLs that hide duplicate query keys, empty tracking params, and half-decoded nested values.
Why Your redirect_uri Breaks: Nested Params, + Signs, and Double Encoding
A practical guide for redirect_uri bugs caused by nested query strings, plus-sign handling, and accidental double encoding across browser and server layers.

Security

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Inspect tokens, generate secrets, and work with hashes and identifiers.

JWT Debugging Checklist: Claims, Expiry, Signatures, and Common Mistakes
A practical JWT troubleshooting guide covering claim inspection, expiry checks, token structure, and adjacent auth debugging steps.