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.
npx agentmods add skills/sd0xdev/sd0x-harness/contract-decodenpx skills add sd0xdev/sd0x-harness --skill contract-decodegit clone --depth 1 https://github.com/sd0xdev/sd0x-harnessWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/sd0xdev/sd0x-harness/contract-decode)<a href="https://agentmods.dev/skills/sd0xdev/sd0x-harness/contract-decode"><img src="https://agentmods.dev/badge/skills/sd0xdev/sd0x-harness/contract-decode.svg" alt="Measured on agentmods" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00053 | $0.01465 |
| Opus 5 | $0.00026 | $0.00732 |
| Sonnet 5 | $0.00011 | $0.00293 |
| Haiku 4.5 | $0.00005 | $0.00146 |
Grade A, and why
contract-decode 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 3d 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.
How it starts
The opening of the file, as written. The whole thing — 188 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Contract Decode — EVM Error & Calldata Decoder
Decode EVM contract function selectors, custom errors, calldata, and revert data.
Trigger
- Keywords: revert, selector, 4byte, calldata, decode, custom error, execution reverted, abi decode
- Message contains
0x+ 8+ hex chars (selector or revert data)
When NOT to Use
- Standard
Error(string)revert already handled by your codebase - Non-EVM chain errors
- Only need error code definitions (not hex decoding)
Input Parsing
Extract from user input:
| Field | Source | Example |
|---|---|---|
revertData |
Error data or user-pasted hex | 0xaca553e4 |
calldata |
Transaction data | 0x5e15c749000...1c05 |
contractAddr |
Contract address | 0x5874...f064 |
chainId |
Chain identifier | 1 (Ethereum mainnet) |
Workflow
Step 1: Classify input → Step 2: Local fast decode → Step 3: ABI query → Step 4: Precise decode → Report
Step 1: Classify Input
| Length | Classification | Next Step |
|---|---|---|
4 bytes (0x + 8 hex) |
Pure selector | Step 2 |
| > 4 bytes, with selector prefix | Calldata or revert data | Step 2 + Step 3 |
| Contract address | Need ABI first | Step 3 |
Step 2: Local Fast Decode (no external dependencies)
Try in order:
2a. Standard error decode
| Selector | Type | Decode Method |
|---|---|---|
0x08c379a0 |
Error(string) |
cast abi-decode "Error(string)" <data> |
0x4e487b71 |
Panic(uint256) |
cast abi-decode "Panic(uint256)" <data> → lookup panic code |
Panic code reference:
| Code | Meaning |
|---|---|
| 0x00 | generic compiler panic |
| 0x01 | assert failure |
| 0x11 | arithmetic overflow |
| 0x12 | division by zero |
| 0x21 | enum conversion |
| 0x22 | storage encoding |
| 0x31 | pop empty array |
| 0x32 | array out of bounds |
| 0x41 | too much memory |
| 0x51 | zero function pointer |
2b. Selector lookup (cast) — optional, skip if cast not installed
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 3d ago First seen · 188 lines · 53 tokens per session scan A 0515628660da
contract-decode is a skill published in the GitHub repository sd0xdev/sd0x-harness (188 stars, last pushed today), licensed MIT. It adds 53 tokens to every session and 1,465 once invoked, about $0.0003 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.
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