Does Arduino IDE 2.x automatically expire its package index cache after a set interval?

Question

Cache behavior in Arduino IDEThe Arduino IDE (both 1.8.x and 2.x) caches package_index.json and library_index.json locally under the Arduino15 directory, reusing them until manually deleted or refreshed via the Board Manager's "Update Index" action. There is no documented time-to-live (TTL) for these caches, nor does the GUI expose a "Clear Cache" button; users must locate and delete the cache files manually, which varies by operating system.Observed symptoms of stale cacheBoard Manager shows outdated board package versionsLibrary Manager lists obsolete library versionsSignature verification failures when upstream metadata changes"Library not found" errors after successful installationThe CLI provides arduino-cli core update-index and arduino-cli lib update-index to force a refresh, but these are not discoverable from the IDE. Third-party board managers (e.g., ESP32, STM32) host their own package indexes with independent update cadences, and corporate HTTP proxies may add another caching layer.Open questionsDoes the IDE or CLI implement any automatic cache expiry (e.g., a 24-hour TTL) for package_index.json or library_index.json?Is there a planned GUI action to clear all caches without manual filesystem access?Do the HTTP requests for package indexes use ETag or If-Modified-Since headers to support conditional GET and cache-busting?

Tasadduq Burney · Answer

AnswerThe IDE 2.x does not automatically purge or refresh the package_index.json and library_index.json files on a timed schedule. The cache remains until the user manually triggers an update or deletes the files.How the Cache WorksBoth Board Manager and Library Manager read the index files from ~/.arduino15 (Linux), %LOCALAPPDATA%/Arduino15 (Windows), or ~/Library/Arduino15 (macOS).When the user clicks Update Index (or uses arduino-cli core update-index / lib update-index), the IDE downloads fresh JSON and overwrites the cached files.Without that action, the IDE reuses the existing files, regardless of how much time has passed.Why No TTL ExistsThe source code and release notes for Arduino IDE 2.x show no implementation of a time‑to‑live (TTL) or background refresh thread for these indexes. The only mechanisms that can change the cached data are:Explicit user action via the GUI’s Update Index button.Command‑line refresh with arduino-cli.Manual deletion of package_index.json or library_index.json – the next manager operation will generate new files.What to Do if You Suspect Stale DataOpen the IDE, note the list of available board and library versions.Close the IDE, locate the index files, and check their modification timestamps.Re‑open the IDE without clicking Update Index and confirm the lists are unchanged.Click Update Index or run arduino-cli core update-index to force a refresh.Missing Diagnostic DetailIf you’re working behind a corporate proxy that may cache HTTP responses, confirm that the proxy is not the source of stale data. The IDE itself does not perform cache invalidation based on server headers.

Does Arduino IDE 2.x automatically expire its package index cache after a set interval?

Cache behavior in Arduino IDE

Observed symptoms of stale cache

Open questions

1 answer

Answer

How the Cache Works

Why No TTL Exists

What to Do if You Suspect Stale Data

Missing Diagnostic Detail

Your perspective belongs here.

0 question comments