wkhtmltopdf can fail with ProtocolUnknownError when file:// URLs are blocked by default, preventing local assets such as stylesheets from loading.

robots.txt can block crawling without removing URLs from search results, while noindex removes accessible pages from indexing. Disallowed URLs may still appear as search matches.

Unique scratch directories prevent flaky tests and stale files in parallel Ruby test runs. Dir.mktmpdir creates them safely and can use a custom base path.

Recover the change history of a deleted file in Git by using git log with history-preserving flags across all references.

Rails 6+ adds before? and after? for comparing dates and times; between? checks whether a value falls within a range.

Growing memory usage in Ruby and Rails can exhaust a process and cause crashes; ObjectSpace.count_objects helps identify leaking object types, and derailed_benchmarks can aid diagnosis.

Rails models often need exactly one of several attributes filled in; built-in validations do not handle this XOR case cleanly. A custom ActiveModel::Validator can enforce blank-or-singleton presence with clear errors.

Convert SVG files to PS, PDF, or EPS without Inkscape using CairoSVG and ps2eps; it is lightweight, fast, and works from files or stdin.

Rails controllers can stay short, testable and authorization-friendly by using a minimal shared blueprint for CRUD, strong params, scopes and optional HTTP caching.

@{-1} resolves to the previous branch name, including when git merge - uses the last checked-out branch.

Running Rails in one file is useful for quick experiments, debugging bugs, or embedding an app in tests, but version and dependency drift can cause surprises.

Chrome can reject locally generated self-signed certificates and hide HTTPS even when they work. Importing the certificate or launching with --ignore-certificate-errors allows testing.

Rails time handling is error-prone because Time.now and Time.current can differ. A single-time-zone setup needs matching Active Record and time zone configuration.

Latency and bandwidth are often confused but affect network performance in different ways: one is delay, the other is data rate.

Local HTTPS for Puma development needs a trusted certificate and SSL binding so Rails runs on https://localhost:3000 without browser warnings.

Duplicate package versions in yarn.lock can bloat bundles and keep unnecessary installs. yarn-deduplicate merges compatible entries in Yarn v1; Yarn v2+ deduplicates natively.

:is() groups selector lists and uses the highest specificity of its arguments, simplifying CSS while avoiding repeated compound selectors.

:where() matches selector lists with zero specificity, simplifying repeated CSS selectors without affecting override behavior; invalid items in the list are ignored.

Find out whether a Rails validation failed by checking ActiveModel::Errors types instead of messages, which is useful in tests and for validations with extra options.

Large ZIP downloads can start immediately without writing files to disk, using zip_tricks_stream for custom content or zipline for existing attachments.

Around hooks run only after Background steps, so setup or teardown placed there cannot affect background actions. Use Before and After hooks instead.

Chrome DevTools shortcuts speed up debugging by toggling the console drawer, adjusting style values faster, and manipulating elements without the mouse.