The Snap provides network params, token list, market data (USD prices), swap quotes, and CCIP bridge routes for these chains. It reads configuration from a token-aggregation (or compatible) API that you supply via apiBaseUrl or optional URL params.

Why this Snap: MetaMask supports Chain 138 as a custom EVM network, but native Swaps, Portfolio Bridge, and USD pricing do not include Chain 138 or ALL Mainnet. This Snap gives in-wallet swap quotes, bridge routes, and market data by calling your token-aggregation API, so users get feature parity on both blockchains without waiting for upstream support.

Features (both blockchains)

Networks & config — EIP-3085 params for Chain 138 and ALL Mainnet (get_networks, get_chain138_config, get_chain138_market_chains).
Token list — By chain; optional chainId (138 or 651940) for get_token_list / get_token_list_url.
Market data — Tokens and USD prices; in-Snap dialog via show_market_data.
Bridge routes — CCIP (WETH9/WETH10) and Trustless (Lockbox) routes to Ethereum Mainnet; dialog via show_bridge_routes.
Swap quote — Quote for Chain 138; dialog via show_swap_quote.
Send (Chain 138) — Companion site Send page (/send) so users can send ETH on Chain 138 without using MetaMask’s in-wallet Send button (which can error with “No XChain Swaps native asset found” on custom chains).
Oracles & dynamic info — API config and in-Snap dialog (get_oracles, show_dynamic_info).

Every method and parameter is documented with tables and diagrams in docs/FEATURES.md (method matrix, params, response shapes, request flow).

Snap ID

Production: npm:chain138-snap

Install from a dApp or the companion site by connecting with MetaMask and adding the Snap with this ID.

Integrators

Snap ID: npm:chain138-snap
Market data, swap quote, bridge routes require the dApp to pass apiBaseUrl (your token-aggregation base URL) when invoking the Snap.
Optional overrides: networksUrl, tokenListUrl, bridgeListUrl (see INTEGRATORS.md).
Companion site: set GATSBY_SNAP_API_BASE_URL for the demo; set SNAP_ORIGIN=npm:chain138-snap for production so the site uses the published Snap.

Testing before publish

For thorough pre-publish testing (build, all RPC methods, logos/images for chain and tokens, companion site, Send page, production-like test, and recommendations), see docs/PRE_PUBLISH_TESTING.md. Quick manual E2E: MANUAL_E2E_CHECKLIST.md and TESTING_INSTRUCTIONS.md.

Troubleshooting (balance, swap, data not showing)

If main balance or USD is not showing, Swap is malfunctioning, or historical/market data does not load, see docs/CHAIN138_SNAP_TROUBLESHOOTING.md. Summary:

$0.00 / no conversion rate: MetaMask has no price feed for Chain 138; use Snap “Show market data” on the companion site or accept quantity-only in the wallet.
In-wallet Swap fails: MetaMask Swap does not support Chain 138; use Send on Chain 138 and swap quotes from the Snap companion site.
Snap market/swap/bridge errors: Ensure GATSBY_SNAP_API_BASE_URL points to a host that serves the token-aggregation API (/api/v1/networks, /api/v1/tokens, /api/v1/quote, etc.); see the troubleshooting doc and FAQ.

Getting started

Clone this repo and run:

pnpm install && pnpm start

Or with Yarn: yarn install && yarn start. See PACKAGE_MANAGER.md.

The companion site and Snap are served at http://localhost:8000. Use MetaMask Flask for development; once the Snap is allowlisted, standard MetaMask can install it.

Documentation

Link	Description
docs/README.md	Documentation index
docs/FEATURES.md	All functions and features — RPC methods, params, both blockchains, tables, flow diagram
INTEGRATORS.md	Integrator guide (Snap ID, apiBaseUrl, RPC list)
TESTING_INSTRUCTIONS.md	Development and E2E testing
docs/FAQ.md	FAQ

Contributing

Lint: pnpm run lint / pnpm run lint:fix
Test: pnpm run test (Snap unit tests), pnpm run test:e2e (Playwright; run npx playwright install once)
See docs/CONTRIBUTING.md and E2E_PREPARATION.md for full setup.

Scripts are disabled by default (LavaMoat). If needed: pnpm run allow-scripts and enable the package in the lavamoat.allowScripts section of package.json. See @lavamoat/allow-scripts.

This Snap targets the latest stable MetaMask Snap SDK (@metamask/snaps-sdk).

README.md Unescape Escape

Chain 138 Snap (MetaMask)