PNG Chunk Inspector
Drop in a PNG to see how it is built. The tool validates the 8-byte signature, then walks every chunk in order and lists its type, length, byte offset, and whether it is critical or ancillary. The file is read entirely in your browser and never uploaded.
How to inspect PNG chunks
- Drag a PNG file onto the box, or click browse to pick one.
- Read the chunk table that appears, showing each type, length, and offset.
- Use the critical and ancillary labels to see which chunks the image needs.
Examples
A simple PNG export
logo.png (a flat PNG with no extra metadata)
3 chunks: IHDR (image header), IDAT (image data), IEND (end)
Frequently asked questions
Is my PNG uploaded anywhere?
No. Nothing is uploaded. The file is read and parsed entirely in your browser using JavaScript, so even sensitive images stay on your device.
What is a PNG chunk?
A PNG file is a signature followed by a stream of chunks. Each chunk has a 4-byte length, a 4-byte type code like IHDR or IDAT, the data itself, and a 4-byte CRC. The chunks together describe the image.
What is the difference between critical and ancillary chunks?
The case of the chunk type's first letter marks it. An uppercase first letter means a critical chunk a decoder must understand, such as IHDR, PLTE, IDAT, and IEND. A lowercase first letter means an ancillary chunk that can be skipped, such as tEXt or pHYs.
What do public and private mean?
The second letter's case marks ownership. An uppercase second letter means a public chunk defined by the PNG specification. A lowercase second letter means a private, application-specific chunk.
Which chunk types does it recognize?
It labels common types including IHDR, PLTE, IDAT, IEND, tEXt, iTXt, zTXt, pHYs, gAMA, sRGB, tRNS, eXIf, and acTL. Unknown types are still listed with their length and offset.
Why does parsing stop at IEND?
IEND marks the end of a PNG datastream, so the inspector stops there. Any bytes after IEND are not part of the image and are ignored.
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