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Agent skill

Message Signing

by Nethereum in Nethereum/Nethereum

Sign and verify Ethereum messages with Nethereum. An agent skill from Nethereum/Nethereum.

MITAuto-check passedBackend & APIs

Install Message Signing

skills CLI
$ npx skills add Nethereum/Nethereum --skill message-signing -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install Nethereum/Nethereum message-signing --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/Nethereum/Nethereum.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/nethereum-skills/skills/message-signing .claude/skills/message-signing && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
message-signing
GitHub stars
2.3k
Token cost
~1k tokens
SKILL.md length
197 words
Files
1
Skills in repo
71
Repo updated
First seen
Licence
MIT

At a glance

Sign and verify Ethereum messages with Nethereum. An agent skill from Nethereum/Nethereum.

  • The user wants to sign a message
  • SKILL.md covers Required Usings, Sign a UTF-8 Message and…, Sign Raw Bytes and Verify External Wallet…, plus 4 more sections
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
  • Verify a signature

What it does

Message Signing is an agent skill from Nethereum/Nethereum. Sign and verify Ethereum messages with Nethereum. Use when the user wants to sign a message, verify a signature, recover a signer address, use personalsign, or implement login-with-Ethereum style authentication.

Its SKILL.md is about 1k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Backend & APIs. It works with Ethereum. The repository describes itself as: Ethereum .Net cross platform integration library. The licence is MIT.

When your agent uses it

  • The user wants to sign a message
  • Verify a signature
  • Recover a signer address
  • Use personalsign

Example prompts

  • “/message-signing”

What it can do on your machine

Read from SKILL.md and the folder at commit 229f278. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md (its code samples are csharp).

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Message Signing loads about 1k tokens when it runs. Until then it costs about 57 tokens; SKILL.md has 197 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~57
When it runs · the whole SKILL.md, loaded when a task matches
~1k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from Nethereum/Nethereum at commit 229f278, republished under its MIT licence (© Nethereum). 197 words, ~1,032 tokens.

Download SKILL.mdSave it as .claude/skills/message-signing/SKILL.md (or your agent's skills folder).
name
message-signing
description
Sign and verify Ethereum messages with Nethereum. Use when the user wants to sign a message, verify a signature, recover a signer address, use personal_sign, or implement login-with-Ethereum style authentication.
user-invocable
true

Message Signing with Nethereum

NuGet: Nethereum.Signer

Source: PersonalSignDocExampleTests, SignerDocExampleTests

Required Usings

csharp
using Nethereum.Signer;
using Nethereum.Util;
using Nethereum.Hex.HexConvertors.Extensions;

Sign a UTF-8 Message and Recover Address

The most common pattern. Signs using the Ethereum personal_sign prefix (\x19Ethereum Signed Message:\n + length).

csharp
var signer = new EthereumMessageSigner();
var message = "Hello from Nethereum";

var signature = signer.EncodeUTF8AndSign(message, new EthECKey(privateKey));

var recoveredAddress = signer.EncodeUTF8AndEcRecover(message, signature);
// recoveredAddress matches the signer's public address

Sign Raw Bytes

Use when the payload is binary rather than a UTF-8 string.

csharp
var signer = new EthereumMessageSigner();
var data = new byte[] { 0x48, 0x65, 0x6c, 0x6c, 0x6f }; // "Hello"

var signature = signer.Sign(data, privateKey);
var recoveredAddress = signer.EcRecover(data, signature);

Assert.True(expectedAddress.IsTheSameAddress(recoveredAddress));

Verify External Wallet Signature (MetaMask, MEW)

Works with any wallet that implements personal_sign. Pass the original message and the hex signature.

csharp
var expectedAddress = "0xe651c5051ce42241765bbb24655a791ff0ec8d13";
var message = "wee test message 18/09/2017 02:55PM";
var signature = "0xf5ac62a395216a84bd595069f1bb79f1ee08a15f07bb9d9349b3b185e69b20c60061dbe5cdbe7b4ed8d8fea707972f03c21dda80d99efde3d96b42c91b2703211b";

var signer = new EthereumMessageSigner();
var recoveredAddress = signer.EncodeUTF8AndEcRecover(message, signature);

Assert.True(expectedAddress.IsTheSameAddress(recoveredAddress));

HashAndSign / HashAndEcRecover Shortcuts

Shorthand that hashes the message before signing. Useful when you want a deterministic hash-based signature without the personal_sign prefix.

csharp
var signer = new EthereumMessageSigner();
var message = "test";

var signature = signer.HashAndSign(message, privateKey);
var recovered = signer.HashAndEcRecover(message, signature);

Assert.True(expectedAddress.IsTheSameAddress(recovered));

Low-S Signature Verification (VerifyAllowingOnlyLowS)

EIP-2 requires the S value of ECDSA signatures to be in the lower half of the curve order. Use VerifyAllowingOnlyLowS for strict validation.

csharp
var ecKey = new EthECKey(privateKey);
var message = "test message";

var signer = new EthereumMessageSigner();
var signature = signer.EncodeUTF8AndSign(message, ecKey);

var prefixedHash = signer.HashPrefixedMessage(message);
var ethSignature = MessageSigner.ExtractEcdsaSignature(signature);

Assert.True(ecKey.VerifyAllowingOnlyLowS(prefixedHash, ethSignature));

EC Key Management

Generate a new key or reconstruct from a known private key.

csharp
// Generate a new random key
var ecKey = EthECKey.GenerateKey();
var privateKeyHex = ecKey.GetPrivateKey();
var publicKeyBytes = ecKey.GetPubKey();
var address = ecKey.GetPublicAddress();

// Reconstruct from existing private key
var reconstructed = new EthECKey(privateKeyHex);
Assert.Equal(address, reconstructed.GetPublicAddress());

Method Reference

MethodPurpose
EncodeUTF8AndSignSign UTF-8 string with personal_sign prefix
EncodeUTF8AndEcRecoverRecover address from UTF-8 signed message
Sign(byte[], key)Sign raw bytes with personal_sign prefix
EcRecover(byte[], sig)Recover address from raw byte signature
HashAndSignHash then sign (no personal prefix)
HashAndEcRecoverHash then recover (no personal prefix)
HashPrefixedMessageGet the prefixed hash without signing
ExtractEcdsaSignatureParse hex signature into ECDSA components
VerifyAllowingOnlyLowSStrict EIP-2 low-S verification

© Nethereum, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in plugins/nethereum-skills/skills/message-signing of Nethereum/Nethereum.

Open the folder on GitHubat commit 229f278

Compare with similar skills

Message Signing next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Message Signing compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Message Signing this skillNethereum/Nethereum2.3k—~1kAutomated safety check: PassMIT
NEAR Intents Swap Integrationinternet-court/internet-court-skill6.4k2 repos~939Automated safety check: PassCustom licence
Deposit QrSuperior-Trade/superior-skills2141 repos~1.1kAutomated safety check: PassMIT
Explorer Contract Verificationsablier-labs/evm-monorepo353—~1.9kAutomated safety check: PassCustom licence
Developing Smart ContractsLFDT-Lineth/lineth-monorepo126—~1.4kAutomated safety check: PassAGPL-3.0
Squash BugbotLFDT-Lineth/lineth-monorepo126—~3.3kAutomated safety check: PassApache-2.0

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Works with

Categories

Questions about Message Signing

What does Message Signing do?

Sign and verify Ethereum messages with Nethereum. An agent skill from Nethereum/Nethereum. Message Signing is an agent skill from Nethereum/Nethereum. Sign and verify Ethereum messages with Nethereum.

When should I use Message Signing?

Message Signing fits situations like: the user wants to sign a message; verify a signature; recover a signer address; use personalsign.

How do I install Message Signing in Claude Code?

Run `npx skills add Nethereum/Nethereum --skill message-signing -a claude-code`. Or copy the skill folder (plugins/nethereum-skills/skills/message-signing in Nethereum/Nethereum) into .claude/skills/message-signing in your project. Claude Code loads it when a task matches its description.

How do I install Message Signing in Codex?

Run `npx skills add Nethereum/Nethereum --skill message-signing -a codex`. Or copy the skill folder (plugins/nethereum-skills/skills/message-signing in Nethereum/Nethereum) into .agents/skills/message-signing in your project. Codex loads it when a task matches its description.

Can I use Message Signing in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add Nethereum/Nethereum --skill message-signing -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/message-signing, .gemini/skills/message-signing, .github/skills/message-signing and .opencode/skills/message-signing in your project.

What does Message Signing need to run?

SKILL.md names no scripts, command-line tools or credentials: Message Signing is instructions for the agent only.

Does Message Signing access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Message Signing safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Message Signing use?

Message Signing is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Message Signing use?

About 1k tokens (SKILL.md is roughly 4.1k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Message Signing?

Skills that share tags, products or a category with Message Signing: NEAR Intents Swap Integration (internet-court/internet-court-skill, 6.4k stars), Deposit Qr (Superior-Trade/superior-skills, 214 stars), Explorer Contract Verification (sablier-labs/evm-monorepo, 353 stars) and Developing Smart Contracts (LFDT-Lineth/lineth-monorepo, 126 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Message Signing?

Nethereum (a GitHub organization) maintains it in Nethereum/Nethereum, which has 2,260 GitHub stars. The repository holds 71 skills in this directory. The repository was last updated on October 5, 2026.

Source: Nethereum/Nethereum on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.