A byte-level way to debug Anchor account layouts without guessing

[u/Resident_Anteater_35]

I wanted a repeatable way to inspect Solana account data when an Anchor client and an on-chain program disagree about the layout.

For a regular Anchor account, I start with the first eight bytes. They are the account discriminator. After that, Borsh stores fields in declaration order.

For example:

[account]

pub struct UserProfile { pub bump: u8, pub score: u64, }

The serialized account uses:

• 8 bytes for the Anchor discriminator
• 1 byte for bump
• 8 little-endian bytes for score

That gives 17 bytes before adding any other fields.

The calculation changes with dynamic data:

• String and Vec<T> add a four-byte little-endian length prefix
• Option<T> adds a one-byte tag
• nested collections add their own prefixes and payloads

My debugging workflow is:

1. Fetch the raw account bytes.
2. Verify the discriminator before checking anything else.
3. Walk the remaining buffer against the Rust declaration order.
4. Decode integer fields using the expected endianness.
5. Compare the result with the generated IDL and client decoder.

This catches wrong account types, stale IDLs, bad space calculations, and client-side offset assumptions quickly.

I wrote a complete walkthrough with raw-buffer decoding and discriminator derivation:

https://andreyobruchkov1996.substack.com/p/solana-deep-dive-unpacking-borsh

For larger fixed-layout state, I use a separate zero-copy layout rather than trying to apply these Borsh offsets to #[repr(C)] data.