diff --git a/README.md b/README.md
index e296278..ce453e2 100644
--- a/README.md
+++ b/README.md
@@ -32,6 +32,7 @@ rome facts balance hadrian 0x…     # native (gas-token) balance for an address
 rome facts programs devnet         # Solana program ids for a network
 rome cookbook cpi-recipe           # the CPI account-rules + SDK encoders (grounded addresses)
 rome cookbook patterns lending     # which example repo + guide fits a goal
+rome cookbook errors "Custom(1)"   # decode a Rome failure → cause + fix (the error taxonomy)
 rome call hadrian 0x… "balanceOf(address) returns (uint256)" 0x…   # read a contract (no key)
 rome doctor hadrian --address 0x…  # preflight: chain live? RPC reachable? program set? wallet funded?
 rome tx hadrian 0x…                # diagnose a tx: EVM receipt + the Solana settlement tx(s) + a Via link
diff --git a/src/core/capabilities.ts b/src/core/capabilities.ts
index 9aac5bd..31cffc7 100644
--- a/src/core/capabilities.ts
+++ b/src/core/capabilities.ts
@@ -1,5 +1,5 @@
 import { getChainFacts, getTokenFacts, getContractFacts, getGasFacts, getBalanceFacts, getProgramFacts } from "./facts.js";
-import { getCpiRecipe, getPatterns } from "./cookbook.js";
+import { getCpiRecipe, getPatterns, getErrors } from "./cookbook.js";
 import { callContract, deployContract, sendContract } from "./actions.js";
 import { fundHandler, bridgeHandler } from "./bridge.js";
 import { doctor } from "./doctor.js";
@@ -107,6 +107,13 @@ export const CAPABILITIES: Capability[] = [
     [{ name: "goal", required: false, description: "optional goal keyword (e.g. lending, amm, oracle)" }],
     (a) => getPatterns(a.goal),
   ),
+  cap(
+    "cookbook",
+    "errors",
+    "Decode a Rome failure → cause + fix (the Rome error taxonomy). A query filters; no query returns the full list.",
+    [{ name: "query", required: false, description: "optional error text / keyword (e.g. Custom(1), gas, cpi, forge)" }],
+    (a) => getErrors(a.query),
+  ),
 
   // ── contract verbs: `call` is a read (CLI+MCP); `deploy`/`send` are CLI-only actions (key) ──
   verbCap(
diff --git a/src/core/cookbook.ts b/src/core/cookbook.ts
index 2485db9..440ff16 100644
--- a/src/core/cookbook.ts
+++ b/src/core/cookbook.ts
@@ -86,3 +86,89 @@ export function getPatterns(goal?: string): Pattern[] {
   );
   return hits.length ? hits : PATTERNS;
 }
+
+export interface ErrorEntry {
+  symptom: string;
+  cause: string;
+  fix: string;
+  tags: string[];
+}
+
+// The net-new Rome error taxonomy — the failure modes a builder/agent actually hits,
+// each as symptom → cause → fix. Rome-specific behaviours that differ from vanilla EVM.
+const ERRORS: ErrorEntry[] = [
+  {
+    symptom: "eth_estimateGas returns a huge value (often 10-50× the real charge); budgets or hard-fails blow up.",
+    cause: "Rome charges the EXACT gas used; the estimate is a loose upper bound, not the amount charged.",
+    fix: "Don't hard-fail or size budgets off the estimate. A plain native-token transfer is ~1.48M gas (not 21k) — use a high fixed gas ceiling and let Rome charge exact.",
+    tags: ["gas", "estimate", "estimategas", "budget", "21000", "out-of-gas"],
+  },
+  {
+    symptom: "A write or eth_estimateGas fails with Custom(1) attributed to the System Program.",
+    cause: "The emulation pool payer is rent-starved — not a fault in your transaction's calldata.",
+    fix: "Retry; if it persists the chain's pool payer needs funding (operator side). Your transaction is fine.",
+    tags: ["custom(1)", "custom1", "system-program", "pool-payer", "estimate", "rent"],
+  },
+  {
+    symptom: "A transaction fails with Custom(0) and no obvious reason.",
+    cause: "An account is TTL-locked (~3-4s) by a concurrent iterative (large) transaction; AccountLocked surfaces as Custom(0).",
+    fix: "Retry after a few seconds once the lock clears. Avoid racing the same account from parallel large transactions.",
+    tags: ["custom(0)", "custom0", "accountlocked", "locked", "iterative", "concurrency", "retry"],
+  },
+  {
+    symptom: "A transaction that does a CPI fails with CpiProhibitedInIterativeTx.",
+    cause: "The transaction was large enough to run in iterative mode, where CPI is prohibited.",
+    fix: "Keep CPI transactions small enough to execute atomically (one Solana tx). Split work so the CPI leg stays under the iterative threshold.",
+    tags: ["cpi", "iterative", "cpiprohibited", "atomic", "size"],
+  },
+  {
+    symptom: "An on-chain call fails with `Program log: Error: UnknownInstruction(N)` and `custom program error: 0x0`.",
+    cause: "The rome-evm program on that chain doesn't implement instruction N — usually a newer feature not yet deployed there.",
+    fix: "That chain's rome-evm program needs an upgrade/redeploy to add the instruction. Confirm the feature is deployed on the chain you're calling.",
+    tags: ["unknowninstruction", "instruction", "0x0", "program-error", "deploy", "upgrade", "settle"],
+  },
+  {
+    symptom: "`forge script` fails in the simulation step before broadcasting.",
+    cause: "Rome's execution model diverges from forge's local EVM simulation.",
+    fix: "Run `forge script --skip-simulation`. `cast` and `forge create` work as-is.",
+    tags: ["forge", "foundry", "script", "simulation", "skip-simulation", "deploy"],
+  },
+  {
+    symptom: "eth_getLogs returns error -32005 (query range too large).",
+    cause: "Rome caps the block range per eth_getLogs query.",
+    fix: "Narrow the fromBlock→toBlock window and page the range.",
+    tags: ["eth_getlogs", "getlogs", "-32005", "32005", "logs", "range", "query"],
+  },
+  {
+    symptom: "A Solana-lane (Phantom / DoTxUnsigned) action fails with Failure(Custom(1)).",
+    cause: "The Solana-lane sender lacks SOL for the on-chain step (the synthetic sender isn't funded with lamports).",
+    fix: "Fund the sender's SOL (swap gas to lamports) before the action; submitRomeTxSolanaLane handles the fund leg when wired.",
+    tags: ["solana-lane", "custom(1)", "phantom", "sol", "lamports", "sender", "dotxunsigned"],
+  },
+  {
+    symptom: "A Wormhole redeem reverts with 'gas limit too high'.",
+    cause: "The VAA was already redeemed.",
+    fix: "Guard with isTransferCompleted before redeeming; treat already-redeemed as success.",
+    tags: ["wormhole", "vaa", "redeem", "gas-limit-too-high", "already-redeemed", "bridge"],
+  },
+  {
+    symptom: "An inbound `fund --intent gas` completes the CCTP legs but native Rome gas never credits (or ends `settle-failed`).",
+    cause: "The final sponsored settle depends on the chain's rome-evm settle instruction; if it's missing/failing the gas conversion can't land.",
+    fix: "Read the transfer's degradationReason for the on-chain error; `--intent wrapper` bypasses the settle (delivers wUSDC). The USDC is always safe in the recipient's account.",
+    tags: ["bridge", "fund", "settle", "gas", "wrapper", "cctp", "from-home", "degradation"],
+  },
+];
+
+/** Decode a Rome failure → cause + fix. No query → the full taxonomy. */
+export function getErrors(query?: string): ErrorEntry[] {
+  if (!query) return ERRORS;
+  const q = query.trim().toLowerCase();
+  const hits = ERRORS.filter(
+    (e) =>
+      e.symptom.toLowerCase().includes(q) ||
+      e.cause.toLowerCase().includes(q) ||
+      e.fix.toLowerCase().includes(q) ||
+      e.tags.some((t) => t.includes(q) || q.includes(t)),
+  );
+  return hits.length ? hits : ERRORS;
+}
diff --git a/test/cookbook-errors.test.ts b/test/cookbook-errors.test.ts
new file mode 100644
index 0000000..cd2f1ed
--- /dev/null
+++ b/test/cookbook-errors.test.ts
@@ -0,0 +1,39 @@
+import { describe, it, expect } from "vitest";
+import { getErrors } from "../src/core/cookbook.js";
+import { CAPABILITIES } from "../src/core/capabilities.js";
+import { buildMcpTools } from "../src/mcp.js";
+
+// `cookbook errors` — the net-new Rome error taxonomy: decode a failure → cause + fix.
+// A read (CLI + MCP), same shape as `cookbook patterns`: filter by query, else the full list.
+
+describe("cookbook errors — the Rome error taxonomy", () => {
+  it("returns the full taxonomy with no query; every entry has symptom/cause/fix", () => {
+    const all = getErrors();
+    expect(all.length).toBeGreaterThanOrEqual(8);
+    for (const e of all) {
+      expect(e.symptom).toBeTruthy();
+      expect(e.cause).toBeTruthy();
+      expect(e.fix).toBeTruthy();
+    }
+  });
+
+  it("filters by symptom / tag", () => {
+    const s = (e: { symptom: string; cause: string; fix: string }) => `${e.symptom} ${e.cause} ${e.fix}`;
+    expect(getErrors("gas").some((e) => /estimate/i.test(s(e)))).toBe(true);
+    expect(getErrors("cpi").some((e) => /iterative/i.test(s(e)))).toBe(true);
+    expect(getErrors("UnknownInstruction").some((e) => /instruction/i.test(e.symptom))).toBe(true);
+  });
+
+  it("falls back to the full list on an unknown query (agent still sees everything)", () => {
+    expect(getErrors("zzzz-nope").length).toBe(getErrors().length);
+  });
+});
+
+describe("cookbook errors is a read capability on MCP", () => {
+  it("registered as a read + present on the MCP surface", () => {
+    const cap = CAPABILITIES.find((c) => c.id === "cookbook.errors");
+    expect(cap?.kind).toBe("read");
+    expect(cap?.requiresKey).toBe(false);
+    expect(new Set(buildMcpTools().map((t) => t.name)).has("cookbook_errors")).toBe(true);
+  });
+});