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.
REST APIs return data in formats that are often compressed, encoded, or timestamped in ways that are difficult to read directly. This guide walks through the most common scenarios you'll encounter and which tools to use for each.
Reading minified JSON responses
API responses are frequently minified to reduce payload size. A response like {"id":1,"status":"active","data":{"items":[1,2,3]}} is valid JSON but difficult to scan visually.
Paste the response into JSON Formatter and press Format. The tool validates the JSON and renders it with proper indentation. If the JSON is invalid, start by fixing the reported parse error before inspecting business fields.
Tools for this section
Decoding Base64-encoded fields
Some APIs embed binary data or tokens as Base64 strings inside JSON, especially for thumbnails, signatures, or attachment fragments. When you see a long opaque string, do not assume it is corrupted immediately.
Copy just that field into Base64 Decoder. If the result becomes readable text, you have found the underlying content. If it still looks binary, the field may legitimately contain an image, PDF, or another file payload.
Tools for this section
Decoding URL-encoded query strings
Webhook URLs and redirect parameters often contain strings like %3A, %2F, and %3D. In raw form they are hard to reason about, especially when tokens or nested URLs are involved.
Use URL Decoder to restore the original value such as https://example.com/path?id=123. If the result still looks wrong, check whether the value has been encoded twice and needs another decode pass.
Tools for this section
Reading timestamp fields
APIs commonly return Unix timestamps in either seconds or milliseconds. Looking at the raw number alone makes it hard to judge event order or time windows.
Timestamp Converter helps you compare UTC, local time, and ISO 8601 instantly. Converting the first and last timestamp in the same response often reveals retry loops, timeout windows, or delayed processing patterns.
Tools for this section
JSON Formatter – Beautify & Pretty Print JSON Online
A high-performance, strictly local JSON formatter and validator with beautiful syntax highlighting. Format or minify your JSON instantly.
Base64 Encoder / Decoder
Encode text or files to Base64, or decode Base64 strings back to plain text.
URL Decoder
Decode percent-encoded URL strings back to human-readable plain text.
Epoch Timestamp Converter
Quickly convert Unix epoch timestamps to human-readable dates and local times, and vice versa.