How I Built StackUtils: A Fast Online JSON Toolkit to Make API Debugging Less Painful

If you work with APIs, logs, webhooks, or configuration files, you probably spend a lot of time staring at JSON.

I certainly do.

Over time I noticed a pattern: whenever I’m debugging an issue, I end up doing the same annoying little dances over and over again:

• Copy a JSON response from the browser’s Network tab
• Paste it into some random “JSON formatter” website
• Open another tab to diff two responses
• Open yet another tab to decode a JWT
• Manually write TypeScript types based on a sample payload

None of these tasks are hard, but they fragment focus. I didn’t want five different sites and a bunch of small scripts just to make sense of data.

So I decided to build a single place for this workflow: StackUtils.

👉 https://stackutils.com

Right now StackUtils is a free, browser-based collection of tools for working with JSON and API-related data. In this story I’ll explain what it does, why I built it, and how it can fit into your daily workflow as a developer or student.

The problem: JSON is everywhere, but tooling is scattered

JSON is the default format for:

• REST API responses
• Webhooks from third-party services
• Log payloads and error reports
• Configuration files and feature flags

But the tools we use to work with JSON are often scattered:

• One site to pretty-print and validate
• Another to diff two responses
• Another to convert JSON to YAML
• Another to decode JWTs
• Another to generate types or models

That’s fine occasionally, but if you’re doing backend, frontend, or API integration work daily, the friction adds up. I wanted something that felt like a small, focused “developer workbench” living right in the browser.

What StackUtils does today

StackUtils lives at:

*https://stackutils.com*

The idea is simple: keep everything client-side, fast, and focused on real workflows. Here’s what it currently includes.

1. JSON viewer & formatter

This is the main tool at (the default view).

• Paste or load any JSON
• See instant validation (valid/invalid with an error message)
• Pretty-print the JSON with indentation
• Minify it back into a single line if needed
• Explore the data in a collapsible tree view

This is my go-to when I have an ugly response from a browser, Postman, or a log file. I paste it into StackUtils, hit “Format”, and then use the tree view to drill into the exact field I care about.

2. JSON ↔ YAML ↔ TOML converter

Config files are not always JSON. Sometimes they’re YAML, sometimes TOML. The converter lets you:

• Use any of JSON/YAML/TOML as the source
• Convert into the other formats
• Keep a single source of truth for the same data

That’s handy when you’re moving between systems (for example, JSON for an API, YAML for Kubernetes, TOML for a tool config).

3. JSON diff

When something breaks after a change, one of the most basic questions is:

“What actually changed in this response?”

The Diff tab lets you paste “before” and “after” JSON and see a structured difference using jsondiffpatch. It’s much easier than visually scanning two blobs in your editor.

4. JSONPath tester

JSONPath is like a query language for JSON. It’s powerful, but a bit abstract until you see it in action.

The JSONPath tester in StackUtils lets you:

• Paste a JSON document
• Write a JSONPath expression (like $.users[*].email)
• Instantly see the results

It’s great for learning JSONPath or testing expressions before you embed them in code, logs, or query tools.

5. JSON Schema: generator + validator

Sometimes you want to go from “sample JSON” to a more formal JSON Schema.

StackUtils helps with:

• Generating a basic schema from an example JSON object
• Validating JSON against any schema using Ajv under the hood

This is useful for documenting APIs, validating inputs, or building contracts between frontend and backend.

6. Config lens (key/path explorer)

Complex config objects can be hard to navigate. The Config lens tool:

• Parses your JSON config
• Extracts all key paths like server.http.port
• Lets you search and copy paths quickly

It’s a small feature, but handy when you’re wiring config through environment variables or layered settings.

7. Mock data generator

If you’re building UI or testing APIs, you often need dummy data.

The Mock data tab lets you:

• Define a simple template JSON object
• Generate N rows of fake data
• Use hints from field names (like name, email, id) to fill in realistic values with Faker

This is useful for seed data, prototypes, and front-end mock states.

8. Log cruncher for NDJSON

Many logging systems produce NDJSON (newline-delimited JSON): one JSON object per line.

The Logs tab allows you to:

• Paste NDJSON logs
• Parse each line into a structured row
• Filter by level (info/error/etc.)
• Search within messages
• Click a row to see the full JSON

It’s a small way to make raw logs more approachable, especially if you’re just grabbing chunks from a file or system like CloudWatch.

9. Token & payload toolbox (JWT, Base64, URL, UUID)

The Tokens tab bundles several utilities:

• JWT decoder (inspect header & payload of tokens)
• Base64 encode/decode
• URL encode/decode
• UUID generator and validator

These are all common operations when dealing with auth, APIs, and IDs. I found myself constantly looking for tiny tools to do these things, so I pulled them into StackUtils.

10. Types generator (TypeScript, C#, Dart)

Finally, there’s a Types tab for turning JSON into code structures:

• Generate TypeScript interfaces
• Generate C# classes
• Generate Dart classes

The goal here isn’t to create perfect production models automatically, but to give you a quick starting point. Paste JSON, choose a language, and get something you can refine instead of writing types from scratch.

Design principles behind StackUtils

While building StackUtils, I tried to follow a few principles:

1. Everything runs in the browser No JSON is sent to a backend. That’s important for privacy and for performance.
2. Fast and minimal The UI is intentionally simple. It’s meant to feel like a utility, not a heavy dashboard.
3. Each tool solves a real, small problem Every tab exists because I’ve personally hit that problem in my own work (and I assume other devs do too).
4. No sign-up required You can use all current tools without creating an account.

Later, I might explore Pro features (like saved collections, cloud sync, endpoint monitoring), but the free toolbox will remain useful on its own.

How you might use StackUtils in your workflow

Here are some concrete ways I imagine other developers using it:

Frontend devs:

• Inspecting API responses from the browser
• Generating TypeScript interfaces from real data
• Debugging differences between staging and production responses

Backend/API devs:

• Validating responses against JSON Schema
• Diffing payloads before and after a code change
• Decoding JWTs and checking claims

DevOps / SRE:

• Parsing NDJSON logs to find a problematic entry
• Converting configs between JSON/YAML/TOML
• Quickly inspecting JSON from log aggregators

Students and learners:

• Exploring what JSON actually looks like in practice
• Playing with JSONPath queries
• Understanding JWT structure and claims

What’s next

StackUtils is still early, and I’m building it incrementally. Some ideas I’m exploring:

• “Learn” sections with interactive examples for JSON, JSONPath, and JWTs
• An HTTP response inspector for quick endpoint checks
• Saved snippets and collections (with optional accounts)
• Endpoint monitors that track response changes over time

But even in its current form, my goal is simple: make it a place where you can paste some JSON and immediately feel like you have control over it.

If tools like this sound useful to you, or you have ideas/feedback, I’d love to hear it.

You can try StackUtils here:

👉 https://stackutils.com

And if you find it handy, consider bookmarking it or sharing it with someone who constantly fights messy JSON in their daily work.