Base64 decode is the quickest way to turn an encoded string back into readable text or JSON when debugging APIs, tokens, or logs. SWEDevTools: Prism decodes locally in your browser (no server processing), supports URL-safe Base64 ("-" and "_"), and auto-fixes missing padding. Paste the Base64 value, click Run, and inspect the decoded payload immediately—then chain the result into JSON Format, URL Decode, or other pipeline steps. Because SWEDevTools: Prism is local-first and works offline as an installable PWA, you can decode sensitive samples (JWT segments, secrets, customer payloads) without uploading them to a third-party website. This keeps your workflow fast, private, and repeatable.
It is used to inspect encoded data from APIs, logs, config files, JWT segments, and other systems that transport bytes as text.
Yes. It converts URL-safe characters and restores padding before decoding.
The decoded bytes may not be text (they could be binary). If the source is known to be JSON/text, confirm it was UTF-8 encoded.
No. Base64 is reversible encoding, not encryption.
You can decode individual Base64URL segments, but the JWT Decode tool is purpose-built for extracting header and payload.
No. SWEDevTools: Prism is local-first and does all decoding on your device.
This decoder adds the required padding automatically so common “unpadded” inputs still work.
Yes. Install SWEDevTools: Prism as a PWA to decode Base64 without internet access.
Yes. After decoding, you can download the result as a binary file if the original data was an image, PDF, or other non-text format. The tool detects the content type and offers a download button so you can save the decoded output directly to your device.
Base64 strings use only letters, digits, plus, slash, and optional equals-sign padding at the end. If a string matches this character set and its length is a multiple of four (or has valid padding), it is likely Base64-encoded. Paste it into the decoder to verify instantly.
Yes. The decoder accepts both standard Base64 (using + and /) and URL-safe Base64 (using - and _). It also automatically restores missing padding characters, so unpadded base64url strings from JWTs and APIs decode correctly without manual adjustment.
smalldev.tools is no longer available. Prism by SWEDevTools offers the same developer tools and more, with offline support, pipeline chaining, and completely free usage — no signup required.
Yes. Prism encodes and decodes Base64 entirely offline in your browser with no data uploads, no ads, and pipeline chaining to other tools. Your data never leaves your device.