agentmods.dev

phantom-sdk-best-practices

A set of coding rules for using Phantom Connect SDKs, which let applications connect to and operate with Phantom wallets. It covers setup, signing, account checks, imports, and error handling.

In plain words
What is it for?
Use it when configuring Phantom in React or JavaScript/TypeScript applications, connecting accounts, signing or sending transactions, and handling rejected wallet prompts.
Why use it?
It helps prevent common integration errors, such as using unsupported signing methods, creating duplicate SDK instances, or attempting wallet actions before connection.

Cursor rule

11 14d ago A scan 313 tokens original MIT
View the source file phantom/phantom-agent-kit
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add rules/phantom/phantom-agent-kit/phantom-sdk-best-practices
Clone the repo
git clone --depth 1 https://github.com/phantom/phantom-agent-kit
Per session 313 This file is loaded in full into every session.
When invoked 313 The same file — it is already loaded in full.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00313 $0.00313
Opus 5 $0.00156 $0.00156
Sonnet 5 $0.00063 $0.00063
Haiku 4.5 $0.00031 $0.00031

Measured 2d ago against content hash 587527065ecd, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

phantom-sdk-best-practices scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

rules/phantom-sdk-best-practices.mdc · 34 lines

What it actually says

Phantom SDK Best Practices

Transaction Signing

  • Always use signAndSendTransaction for sending transactions. NEVER use signTransaction — it is NOT supported for embedded wallets and will throw an error.

Provider Setup

  • In React apps, always wrap the application root in PhantomProvider with a valid config object containing appId, providers, and addressTypes.
  • In vanilla JS/TS apps, initialize a single BrowserSDK instance and reuse it as a singleton throughout the application. Never create multiple instances.

Error Handling

  • Always wrap connect(), signAndSendTransaction(), signMessage(), and other async SDK calls in try-catch blocks. Users can reject prompts at any time.

Connection State

  • Always check isConnected or verify account availability before attempting signing or transaction operations.
  • Access accounts via useAccounts() hook (React) or sdk.accounts (Browser SDK) and filter by chain property.

Imports

  • Import AddressType from @phantom/browser-sdk when using the Browser SDK. Do not import it from other packages.

App Registration

  • Always register your app in Phantom Portal and use a real appId. Social login and embedded wallet features require a valid appId.
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 34 lines · 313 tokens per session scan A 587527065ecd

Subscribe to this mod's changes

phantom-sdk-best-practices is a cursor rule published in the GitHub repository phantom/phantom-agent-kit (11 stars, last pushed 14d ago), licensed MIT. It adds 313 tokens to every session, about $0.0016 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

FrontendLanguages
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