Fizz Convert
pashov/skills
Convert English-language properties in PROPERTIES.md (produced by the Fizz skill) into Solidity assertions inside the existing fuzz harness, then flip their checkboxes.
Provides guidance for property-based testing across multiple languages and smart contracts.
Install Property Based Testing
$ npx skills add CraftOS-dev/CraftBot --skill property-based-testing -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install CraftOS-dev/CraftBot property-based-testing --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/CraftOS-dev/CraftBot.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/property-based-testing .claude/skills/property-based-testing && rm -rf skills-srcUse ~/.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/
Install the "property-based-testing" agent skill from https://github.com/CraftOS-dev/CraftBot/tree/main/skills/property-based-testing into .claude/skills/property-based-testing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "property-based-testing", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/CraftOS-dev/CraftBot/tree/main/skills/property-based-testingType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add CraftOS-dev/CraftBot --skill property-based-testing -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install CraftOS-dev/CraftBot property-based-testing --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/CraftOS-dev/CraftBot.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/property-based-testing .agents/skills/property-based-testing && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "property-based-testing" agent skill from https://github.com/CraftOS-dev/CraftBot/tree/main/skills/property-based-testing into .agents/skills/property-based-testing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "property-based-testing", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add CraftOS-dev/CraftBot --skill property-based-testing -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install CraftOS-dev/CraftBot property-based-testing --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/CraftOS-dev/CraftBot.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/property-based-testing .cursor/skills/property-based-testing && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "property-based-testing" agent skill from https://github.com/CraftOS-dev/CraftBot/tree/main/skills/property-based-testing into .cursor/skills/property-based-testing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "property-based-testing", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/CraftOS-dev/CraftBot.git --path skills/property-based-testing--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add CraftOS-dev/CraftBot --skill property-based-testing -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install CraftOS-dev/CraftBot property-based-testing --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/CraftOS-dev/CraftBot.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/property-based-testing .gemini/skills/property-based-testing && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "property-based-testing" agent skill from https://github.com/CraftOS-dev/CraftBot/tree/main/skills/property-based-testing into .gemini/skills/property-based-testing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "property-based-testing", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install CraftOS-dev/CraftBot property-based-testingInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add CraftOS-dev/CraftBot --skill property-based-testing -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/CraftOS-dev/CraftBot.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/property-based-testing .github/skills/property-based-testing && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "property-based-testing" agent skill from https://github.com/CraftOS-dev/CraftBot/tree/main/skills/property-based-testing into .github/skills/property-based-testing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "property-based-testing", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add CraftOS-dev/CraftBot --skill property-based-testing -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install CraftOS-dev/CraftBot property-based-testing --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/CraftOS-dev/CraftBot.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/property-based-testing .opencode/skills/property-based-testing && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "property-based-testing" agent skill from https://github.com/CraftOS-dev/CraftBot/tree/main/skills/property-based-testing into .opencode/skills/property-based-testing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "property-based-testing", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
property-based-testing- GitHub stars
- 392
- Token cost
- ~1.5k tokens
- SKILL.md length
- 513 words
- Files
- 9 (incl. references)
- Skills in repo
- 89
- Repo updated
- First seen
- Licence
- MIT
At a glance
Provides guidance for property-based testing across multiple languages and smart contracts.
- Reviewing code with serialization/validation/parsing patterns
- SKILL.md covers When to Invoke (Automatic…, When NOT to Use, Property Catalog (Quick… and Decision Tree, plus 4 more sections
- Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
- Designing features
What it does
Property Based Testing is an agent skill from CraftOS-dev/CraftBot. Provides guidance for property-based testing across multiple languages and smart contracts. Use when writing tests, reviewing code with serialization/validation/parsing patterns, designing features, or when property-based testing would provide stronger coverage than example-based tests.
Its SKILL.md is about 1.5k tokens, which your agent loads only when the skill is triggered. The skill folder holds 9 other files, including reference files (for example `README.md`, `references/design.md` and `references/generating.md`).
It sits in Backend & APIs, covering Smart contracts. The repository describes itself as: One agent. Every kind of work. The licence is MIT.
When your agent uses it
- Reviewing code with serialization/validation/parsing patterns
- Designing features
- Property-based testing would provide stronger coverage than example-based tests
Example prompts
- “Use the property-based-testing skill to provide guidance for property-based testing across multiple languages and smart contracts”
- “/property-based-testing”
What it can do on your machine
Read from SKILL.md and the folder at commit b50970c. 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.
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
Property Based Testing loads about 1.5k tokens when it runs, and up to ~11k if it reads all its reference files. Until then it costs about 78 tokens; SKILL.md has 513 words of instructions outside code blocks.
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 CraftOS-dev/CraftBot at commit b50970c, republished under its MIT licence (© CraftOS-dev). 513 words, ~1,516 tokens.
Download SKILL.mdSave it as
.claude/skills/property-based-testing/SKILL.md (or your agent's skills folder). This skill also uses 8 other files; get the full folder from GitHub.- name
- property-based-testing
- description
- Provides guidance for property-based testing across multiple languages and smart contracts. Use when writing tests, reviewing code with serialization/validation/parsing patterns, designing features, or when property-based testing would provide stronger coverage than example-based tests.
Property-Based Testing Guide
Use this skill proactively during development when you encounter patterns where PBT provides stronger coverage than example-based tests.
When to Invoke (Automatic Detection)
Invoke this skill when you detect:
- Serialization pairs:
encode/decode,serialize/deserialize,toJSON/fromJSON,pack/unpack - Parsers: URL parsing, config parsing, protocol parsing, string-to-structured-data
- Normalization:
normalize,sanitize,clean,canonicalize,format - Validators:
is_valid,validate,check_*(especially with normalizers) - Data structures: Custom collections with
add/remove/getoperations - Mathematical/algorithmic: Pure functions, sorting, ordering, comparators
- Smart contracts: Solidity/Vyper contracts, token operations, state invariants, access control
Priority by pattern:
| Pattern | Property | Priority |
|---|---|---|
| encode/decode pair | Roundtrip | HIGH |
| Pure function | Multiple | HIGH |
| Validator | Valid after normalize | MEDIUM |
| Sorting/ordering | Idempotence + ordering | MEDIUM |
| Normalization | Idempotence | MEDIUM |
| Builder/factory | Output invariants | LOW |
| Smart contract | State invariants | HIGH |
When NOT to Use
Do NOT use this skill for:
- Simple CRUD operations without transformation logic
- One-off scripts or throwaway code
- Code with side effects that cannot be isolated (network calls, database writes)
- Tests where specific example cases are sufficient and edge cases are well-understood
- Integration or end-to-end testing (PBT is best for unit/component testing)
Property Catalog (Quick Reference)
| Property | Formula | When to Use |
|---|---|---|
| Roundtrip | decode(encode(x)) == x | Serialization, conversion pairs |
| Idempotence | f(f(x)) == f(x) | Normalization, formatting, sorting |
| Invariant | Property holds before/after | Any transformation |
| Commutativity | f(a, b) == f(b, a) | Binary/set operations |
| Associativity | f(f(a,b), c) == f(a, f(b,c)) | Combining operations |
| Identity | f(x, identity) == x | Operations with neutral element |
| Inverse | f(g(x)) == x | encrypt/decrypt, compress/decompress |
| Oracle | new_impl(x) == reference(x) | Optimization, refactoring |
| Easy to Verify | is_sorted(sort(x)) | Complex algorithms |
| No Exception | No crash on valid input | Baseline property |
Strength hierarchy (weakest to strongest): No Exception → Type Preservation → Invariant → Idempotence → Roundtrip
Decision Tree
Based on the current task, read the appropriate section:
TASK: Writing new tests
→ Read [{baseDir}/references/generating.md]({baseDir}/references/generating.md) (test generation patterns and examples)
→ Then [{baseDir}/references/strategies.md]({baseDir}/references/strategies.md) if input generation is complex
TASK: Designing a new feature
→ Read [{baseDir}/references/design.md]({baseDir}/references/design.md) (Property-Driven Development approach)
TASK: Code is difficult to test (mixed I/O, missing inverses)
→ Read [{baseDir}/references/refactoring.md]({baseDir}/references/refactoring.md) (refactoring patterns for testability)
TASK: Reviewing existing PBT tests
→ Read [{baseDir}/references/reviewing.md]({baseDir}/references/reviewing.md) (quality checklist and anti-patterns)
TASK: Test failed, need to interpret
→ Read [{baseDir}/references/interpreting-failures.md]({baseDir}/references/interpreting-failures.md) (failure analysis and bug classification)
TASK: Need library reference
→ Read [{baseDir}/references/libraries.md]({baseDir}/references/libraries.md) (PBT libraries by language, includes smart contract tools)Show full SKILL.md (244 more words)Show less
How to Suggest PBT
When you detect a high-value pattern while writing tests, offer PBT as an option:
"I notice
encode_message/decode_messageis a serialization pair. Property-based testing with a roundtrip property would provide stronger coverage than example tests. Want me to use that approach?"
If codebase already uses a PBT library (Hypothesis, fast-check, proptest, Echidna), be more direct:
"This codebase uses Hypothesis. I'll write property-based tests for this serialization pair using a roundtrip property."
If user declines, write good example-based tests without further prompting.
When NOT to Use PBT
- Simple CRUD without complex validation
- UI/presentation logic
- Integration tests requiring complex external setup
- Prototyping where requirements are fluid
- User explicitly requests example-based tests only
Red Flags
- Recommending trivial getters/setters
- Missing paired operations (encode without decode)
- Ignoring type hints (well-typed = easier to test)
- Overwhelming user with candidates (limit to top 5-10)
- Being pushy after user declines
Rationalizations to Reject
Do not accept these shortcuts:
- "Example tests are good enough" - If serialization/parsing/normalization is involved, PBT finds edge cases examples miss
- "The function is simple" - Simple functions with complex input domains (strings, floats, nested structures) benefit most from PBT
- "We don't have time" - PBT tests are often shorter than comprehensive example suites
- "It's too hard to write generators" - Most PBT libraries have excellent built-in strategies; custom generators are rarely needed
- "The test failed, so it's a bug" - Failures require validation; see interpreting-failures.md
- "No crash means it works" - "No exception" is the weakest property; always push for stronger guarantees
© CraftOS-dev, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
SKILL.md and 8 other files (references) in skills/property-based-testing of CraftOS-dev/CraftBot.
- SKILL.md
- README.md
- references/design.md
- references/generating.md
- references/interpreting-failures.md
- references/libraries.md
- references/refactoring.md
- references/reviewing.md
- references/strategies.md
Open the folder on GitHubat commit b50970c
Compare with similar skills
Property Based Testing 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.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Property Based Testing this skillCraftOS-dev/CraftBot | 392 | — | ~1.5k | Automated safety check: Pass | MIT | |
| Fizz Convertpashov/skills | 1.2k | 2 repos | ~3.7k | Automated safety check: Pass | MIT | |
| Solana Devsolana-foundation/solana-dev-skill | 571 | — | ~3.8k | Automated safety check: Pass | MIT | |
| Feynman Auditor0xiehnnkta/nemesis-auditor | 244 | 1 repos | ~11k | Automated safety check: Pass | MIT | |
| Smart Contract Auditgreatpie/smart-contract-audit-skill | 101 | — | ~1.1k | Automated safety check: Pass | None | |
| RadarAuditware/radar | 154 | — | ~2.1k | Automated safety check: Pass | GPL-3.0 |
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Categories
Questions about Property Based Testing
What does Property Based Testing do?
Provides guidance for property-based testing across multiple languages and smart contracts. Property Based Testing is an agent skill from CraftOS-dev/CraftBot. Provides guidance for property-based testing across multiple languages and smart contracts.
When should I use Property Based Testing?
Property Based Testing fits situations like: reviewing code with serialization/validation/parsing patterns; designing features; property-based testing would provide stronger coverage than example-based tests.
How do I install Property Based Testing in Claude Code?
Run `npx skills add CraftOS-dev/CraftBot --skill property-based-testing -a claude-code`. Or copy the skill folder (skills/property-based-testing in CraftOS-dev/CraftBot) into .claude/skills/property-based-testing in your project. Claude Code loads it when a task matches its description.
How do I install Property Based Testing in Codex?
Run `npx skills add CraftOS-dev/CraftBot --skill property-based-testing -a codex`. Or copy the skill folder (skills/property-based-testing in CraftOS-dev/CraftBot) into .agents/skills/property-based-testing in your project. Codex loads it when a task matches its description.
Can I use Property Based Testing 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 CraftOS-dev/CraftBot --skill property-based-testing -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/property-based-testing, .gemini/skills/property-based-testing, .github/skills/property-based-testing and .opencode/skills/property-based-testing in your project.
What does Property Based Testing need to run?
SKILL.md names no scripts, command-line tools or credentials: Property Based Testing is instructions for the agent only.
Does Property Based Testing 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 Property Based Testing 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 Property Based Testing use?
Property Based Testing 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 Property Based Testing use?
About 1.5k tokens (SKILL.md is roughly 6.1k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 9k tokens, read only when the agent opens those files.
What are the alternatives to Property Based Testing?
Skills that share tags, products or a category with Property Based Testing: Fizz Convert (pashov/skills, 1.2k stars), Solana Dev (solana-foundation/solana-dev-skill, 571 stars), Feynman Auditor (0xiehnnkta/nemesis-auditor, 244 stars) and Smart Contract Audit (greatpie/smart-contract-audit-skill, 101 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Property Based Testing?
CraftOS-dev (a GitHub user) maintains it in CraftOS-dev/CraftBot, which has 392 GitHub stars. The repository holds 89 skills in this directory. The repository was last updated on October 7, 2026.
Source: CraftOS-dev/CraftBot on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.