Crate llm_message_hash 

llm-message-hash

Stable canonical hash of LLM request/message structures.

Two semantically-identical Anthropic requests can produce different sha256(serde_json::to_string(&req)) results because:

• JSON key order isn’t guaranteed.
• cache_control fields don’t change request semantics but change the bytes.
• Optional metadata (metadata.user_id, etc.) varies between callers.

This crate fixes that. It walks the value tree, sorts keys recursively, drops a configurable set of fields, and sha256s the canonical bytes.

Quick example

use serde_json::json;
use llm_message_hash::{hash_canonical_hex, HashOpts};

let a = json!({
    "model": "claude-sonnet-4-5",
    "messages": [{"role": "user", "content": "hi"}],
});
let b = json!({
    "messages": [{"content": "hi", "role": "user"}],
    "model": "claude-sonnet-4-5",
});

assert_eq!(hash_canonical_hex(&a), hash_canonical_hex(&b));

With per-provider ignore lists

use serde_json::json;
use llm_message_hash::{hash_canonical_hex_with, HashOpts};

let req_a = json!({
    "model": "claude-sonnet-4-5",
    "messages": [{
        "role": "user",
        "content": [{"type": "text", "text": "hi", "cache_control": {"type": "ephemeral"}}],
    }],
});
let req_b = json!({
    "model": "claude-sonnet-4-5",
    "messages": [{
        "role": "user",
        "content": [{"type": "text", "text": "hi"}],
    }],
});

// `HashOpts::anthropic()` drops cache_control + metadata.user_id
let h1 = hash_canonical_hex_with(&req_a, &HashOpts::anthropic());
let h2 = hash_canonical_hex_with(&req_b, &HashOpts::anthropic());
assert_eq!(h1, h2);

Structs

HashOpts

Tunables for hash_canonical_with.

Functions

hash_canonical

sha256 of the canonical JSON representation of v with default options (no fields ignored).

hash_canonical_hex

Hex-encoded sha256 of the canonical JSON representation of v with default options.

hash_canonical_hex_with

Hex-encoded sha256 of the canonical JSON representation of v, honoring opts.

hash_canonical_with

sha256 of the canonical JSON representation of v, honoring opts.