What are critical vs ancillary chunks?

Critical chunks (IHDR, PLTE, IDAT, IEND — first letter uppercase) must be understood by a decoder for the image to render. Ancillary chunks (lowercase first letter, e.g. `tEXt`, `pHYs`, `tIME`) carry metadata that decoders can safely ignore.

Where do `tEXt` keys come from?

Standard registered keys are `Title`, `Author`, `Description`, `Copyright`, `Creation Time`, `Software`, `Disclaimer`, `Warning`, `Source`, `Comment`. Editors usually write `Software` (the name of the editor) and sometimes private custom keys.

PNG Chunk Inspector

File

A PNG file is a magic 8-byte signature followed by a sequence of chunks. Each chunk has a length, a 4-letter type code, payload bytes, and a 32-bit CRC. The case of each letter in the type encodes flags — uppercase first letter is `critical` (the decoder must handle it), lowercase is `ancillary`. This inspector parses the whole file in the browser, lists every chunk with its meta, surfaces the IHDR header (dimensions, color type, bit depth), and decodes any `tEXt` / `iTXt` metadata blocks — common places editors hide signatures, copyrights, or camera notes.

—

How to use

Drop a `.png` file. The IHDR summary and chunk list appear immediately.
The chunk table shows the 4-letter type, payload length, and the four type-bit flags.
Any `tEXt` / `iTXt` metadata is decoded at the bottom — useful for spotting embedded copyright tags or editor signatures.

Frequently asked questions

What are critical vs ancillary chunks?: Critical chunks (IHDR, PLTE, IDAT, IEND — first letter uppercase) must be understood by a decoder for the image to render. Ancillary chunks (lowercase first letter, e.g. `tEXt`, `pHYs`, `tIME`) carry metadata that decoders can safely ignore.
Where do `tEXt` keys come from?: Standard registered keys are `Title`, `Author`, `Description`, `Copyright`, `Creation Time`, `Software`, `Disclaimer`, `Warning`, `Source`, `Comment`. Editors usually write `Software` (the name of the editor) and sometimes private custom keys.

Related tools

Image → PDF Converter

Combine multiple JPG / PNG images into a single PDF with adjustable page size, orientation, and fit.

File00

ZIP Inspector

Drop a ZIP and see every file inside — sizes, contents, and per-file download — without unpacking it locally.

File00

File Splitter

Split a large file into smaller chunks to bypass attachment or upload size limits.

File00

Text Encoding Converter

Open text files in legacy encodings (EUC-KR, Shift_JIS, Windows-1252…) as readable UTF-8.

File00

File Hash (Checksum)

Compute SHA-1, SHA-256, and SHA-512 checksums of any file.

File00

CSV ↔ JSON Converter

Convert CSV to JSON and JSON back to CSV, with a delimiter option.

File00