The #[program] Module

The #[program] attribute macro generates Solana's entrypoint, instruction dispatch, and discriminator checks. Your public functions become on-chain instructions.

Recipe

#[program]
pub mod my_program {
    use super::*;
 
    pub fn initialize(ctx: Context<Initialize>, amount: u64) -> Result<()> {
        ctx.accounts.config.amount = amount;
        Ok(())
    }
}

When to reach for this: You add or rename an instruction exposed to clients.

Working Example

use anchor_lang::prelude::*;
 
declare_id!("Fg6PaFpoGXkYsidMpWTK6W2BeZ7FEfcYkg476zPFsLnS");
 
#[program]
pub mod escrow {
    use super::*;
 
    pub fn initialize(ctx: Context<Initialize>, amount: u64) -> Result<()> {
        let escrow = &mut ctx.accounts.escrow;
        escrow.amount = amount;
        escrow.authority = ctx.accounts.authority.key();
        Ok(())
    }
 
    pub fn release(ctx: Context<Release>) -> Result<()> {
        require!(ctx.accounts.authority.key() == ctx.accounts.escrow.authority, EscrowError::Unauthorized);
        // transfer logic ...
        Ok(())
    }
}
 
#[account]
pub struct Escrow {
    pub amount: u64,
    pub authority: Pubkey,
}
 
#[derive(Accounts)]
pub struct Initialize<'info> {
    #[account(init, payer = authority, space = 8 + Escrow::INIT_SPACE)]
    pub escrow: Account<'info, Escrow>,
    #[account(mut)]
    pub authority: Signer<'info>,
    pub system_program: Program<'info, System>,
}
 
#[derive(Accounts)]
pub struct Release<'info> {
    #[account(mut, has_one = authority)]
    pub escrow: Account<'info, Escrow>,
    pub authority: Signer<'info>,
}

What this demonstrates:

• Module name becomes the program module namespace in clients
• Each pub fn is one instruction with a unique discriminator
• Account structs are separate #[derive(Accounts)] types
• Return Result<()> for fallible instructions

Deep Dive

How It Works

• Anchor hashes the instruction name to an 8-byte discriminator prepended to instruction data.
• The generated dispatcher deserializes accounts into your Context<T> struct.
• Private functions inside the module are not exposed as instructions.
• use super::*; brings account structs and types into scope.

Handler Signatures

Gotchas

• Handler named init - Conflicts with reserved patterns in some tooling.. Fix: Use initialize instead.
• Account struct inside #[program] - Macro cannot find types reliably.. Fix: Define #[derive(Accounts)] at module root.
• Missing use super::* - Types not in scope inside module.. Fix: Add the import at top of program module.
• Pub fn with wrong Context type - Dispatch passes wrong account layout.. Fix: Match struct name to Context<StructName>.
• Returning non-Result - Only Result and return-data patterns compile for handlers.. Fix: Use Result<()> unless returning data explicitly.

Alternatives

FAQs

Related

• Instruction Handlers - Context and signatures
• The Accounts Struct - validation structs
• Building & Deploying - build output

Stack versions: This page was written for Agave 4.1.1, Solana CLI 3.0.10, Anchor 0.32.1, anchor-lang 0.32.1, Rust 1.91.1, @solana/kit 7.0.0, Surfpool 0.12.0, and LiteSVM 0.6.x.