Soulbound Credentials on Solana: Building Revocable Tokens with Non-Transferable + Permanent Delegate

I spent 7 days learning Solana token extensions. Here's what clicked, what surprised me, and the code you need to build tokens that can't be traded but can be revoked. The Problem (In Web2 Terms) Imagine you work in HR. You issue an employee a digital badge proving they're a certified security officer. Here's what you'd want: The badge stays in their wallet — they can't trade or sell it Only they can use it If they leave the company or fail a compliance check, you can revoke it silently without their permission The badge metadata (name, symbol, type) is on-chain and permanent You could build this with centralized databases and APIs. On Solana, it's just three extensions on a token mint . What Are Token Extensions? Solana's Token-2022 program lets you attach additional behaviors to any mint at creation time. Think of them like middleware for tokens. Before extensions, every token was the same — a mint with supply and decimals, token accounts holding balances, and transfer instructions. Extensions let you add rules on top : Extension What It Does Use Case Transfer Fee Charge a percentage on every transfer Protocol revenue, marketplace commissions Non-Transferable Make tokens unmovable after minting Soulbound badges, credentials, memberships Permanent Delegate Let the issuer burn tokens from anyone Revocable credentials, subscriptions with expiry Metadata Store name, symbol, URI on-chain Self-describing tokens, no external API needed Default Account State Freeze all new accounts by default Compliance gates, KYC verification The critical rule: extensions must be declared at mint creation . You cannot add them later. This forces you to think about your token's full lifecycle before deploying — which is good design discipline. The Journey: Three Combinations That Matter Over the past week I built three different token types. Here's what I learned from each. Day 34: Transfer Fees (The Marketplace Token) A token that charges 1% on every transfer, withheld automatically and