- Minimize new code and changes. Prefer the first working option:
- Skip if unnecessary
- Reuse existing code
- Use native platform features
- Write it one line if that is clear and correct
- Use standard library
- Use existing library
- Use popular, modern, minimal, fast library
- Write the minimum code that works
- Prefer deletion over addition, boring over clever, 1 file over many. Minimize abstractions, scaffolding, or dependencies
- Prefer data over code: structures beat conditionals. Prefer config.{json|yaml|toml|...} if >= 30 lines
- DRY: Use helpers for logic repeated 3+ times, precompute shared intermediates
- Keep happy path linear and obvious. Write flow first, then fill in code
- Early returns fail fast and reduce nesting. Skip defensive fallbacks, existence checks, ... unless essential
- Change existing code minimally. Retain existing comments. Follow existing style
- Make scripts re-startable if interrupted
Docs:
- Use type hints and docstrings (document contracts and surprises, not mechanics)
- Comment non-obvious stuff that'll trip future maintainers: why, why not alternatives, pitfalls, invariants, input/output shape, ...
Tests:
- When tests exist, or writing new code, add and run tests first (including edge cases). Keep tests fast
- Test final outputs, not just the source / intermediates
- Test visual artifacts (web pages, docs, slides, PDFs, ...) with screenshots (for responsive layout, overlaps, contrast & visibility) AND DOM (for interactions, navigation, accessibility) before finalizing
- Never say "verified" without evidence. List changes, validations with results, and remaining risks/unknowns
Ops:
- Log status & progress for long tasks (>5s). Log before action. Flush logs
Bug fixes:
- Fix the root cause, not just the reported symptom. Check callers before patching
Python
Prefer uv run --with pkg1 --with pkg2 script.py, uvx --from pkg cmd over python or python3
Avoid requirements.txt. Unless pyproject.toml is present, add dependencies as PEP 723 metadata:
#!/usr/bin/env -S uv run --script
# /// script
# requires-python = ">=3.14"
# dependencies = ["scipy>=1.10", "httpx"]
# ///
Prefer:
- typer / click not argparse
- httpx not requests
- lxml not xml
- duckdb / pandas not csv
- tenacity for retries
HTML
Prefer modern HTML:
- Loading: loading="lazy", fetchpriority="low", <link rel="preload" as="image">
- Forms: inputmode=, enterkeyhint=, autocomplete=, list=, autocapitalize=, spellcheck=, form=
- UI: popover, popovertarget=, formmethod="dialog", inert, <details name=""> for accordions, <dialog>, <meter>, <progress>, <track>, <data>
- Media: picture srcset=, video preload=, crossorigin=, playsinline=, muted=, autoplay=, loop=, controls=, poster=
JavaScript
Preferred JS style:
- Hyphenated HTML class/ID names (id="user-id" not id="userId")
- Modern browser APIs and ESM2022+: Use
?.,??, destructuring, spread, implicit returns (=>over=> { return }) - No TypeScript, but
// @ts-check..d.tsis OK for packages - Loading indicator while awaiting fetch()
- Error handling only at top level. Render errors for user
Debug front-end apps with agent-browser, rodney, Playwright via CDP on localhost:9222.
For single-page HTML files try file:// if a server may not be needed.