Postconditions: what we check

• Redis · missing-error-listener

  error
  WhenRedis instance created without error event listener
  ThrowsErrors emitted as events, not exceptions - silent failures
  Required handlingCaller MUST attach an error listener immediately after creating Redis instance: `redis.on('error', (err) => logger.error(err))`. Without this listener, connection errors are silently logged to console and may crash the application.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[1]
• Redis · connection-errors-not-handled

  error
  WhenConnection fails (ECONNREFUSED, ETIMEDOUT, ECONNRESET, ENOTFOUND, EPIPE, EAI_AGAIN)
  ThrowsError event emitted with connection error
  Required handlingCaller MUST handle connection errors in the error event listener. Common errors: ECONNREFUSED (Redis not running), ETIMEDOUT (network timeout), ECONNRESET (connection dropped), ENOTFOUND (DNS failure).
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[2]
• get · unhandled-promise-rejection

  error
  WhenCommand promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning - will crash in future Node.js versions
  Required handlingCaller MUST use try-catch (async/await) or .catch() on all Redis commands. Commands return promises that may reject due to: connection errors, WRONGTYPE, timeout, or serialization failures.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[3]
• get · command-timeout

  warning
  WhenCommand exceeds timeout (default: no timeout)
  ThrowsMaxRetriesPerRequestError or CommandTimeoutError
  Required handlingCaller SHOULD set commandTimeout option to prevent hanging operations. Without timeout, commands may hang indefinitely on network issues.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[4]
• set · unhandled-promise-rejection

  error
  WhenCommand promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning
  Required handlingCaller MUST use try-catch or .catch() on all Redis commands.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[3]
• pipeline · pipeline-results-not-checked

  error
  WhenPipeline exec() results not checked for errors
  ThrowsIndividual command errors silently included in results array
  Required handlingCaller MUST check each result in pipeline.exec() return value. Format: [[null, 'OK'], [Error, undefined], ...]. Pipeline does NOT reject on individual command failures.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[5]
• pipeline · pipeline-exec-unhandled

  error
  WhenPipeline exec() promise rejected without catch
  ThrowsUnhandledPromiseRejectionWarning
  Required handlingCaller MUST use try-catch or .catch() on pipeline.exec().
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[6]
• multi · watch-null-not-checked

  error
  WhenWATCH violation causes exec() to return null, not checked
  Throwsnull return value indicates transaction was aborted
  Required handlingCaller MUST check if exec() returns null after using WATCH. Null indicates a watched key was modified, transaction aborted. This is NOT an error/rejection - it's a null return value.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[7]
• multi · exec-abort-not-handled

  error
  WhenEXECABORT error in transaction not handled
  ThrowsEXECABORT error if queued command fails validation
  Required handlingCaller MUST check exec() results for EXECABORT errors. Happens when queued commands fail validation (WRONGTYPE, etc.).
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[8]
• subscribe · subscriber-mode-violation

  error
  WhenNon-pub/sub commands used on subscriber connection
  ThrowsError: Connection in subscriber mode, only subscriber commands allowed
  Required handlingCaller MUST use separate Redis connection for pub/sub. After subscribe(), only subscribe/unsubscribe/psubscribe/punsubscribe/quit/ping allowed. Use redis.duplicate() to create separate connection for normal commands.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[9]
• brpop · blocking-without-timeout

  warning
  WhenBlocking command without timeout parameter
  ThrowsCommand may block indefinitely, causing resource leak
  Required handlingCaller SHOULD provide timeout parameter to blocking commands (BRPOP, BLPOP, BZPOPMIN, BZPOPMAX). Without timeout (or timeout=0), command blocks until data available, potentially forever. Recommended: Set reasonable timeout (e.g., 5-30 seconds).
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[10]
• connect · connect-promise-unhandled

  error
  Whenconnect() promise rejected without catch
  ThrowsUnhandledPromiseRejectionWarning on connection failure
  Required handlingCaller MUST use try-catch or .catch() on explicit connect() calls.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[11]
• hget · wrong-type-error

  error
  WhenKey exists but is not a hash
  ThrowsReplyError with message containing 'WRONGTYPE'
  Required handlingCaller MUST catch WRONGTYPE errors for hash operations. This indicates key is not a hash - DO NOT retry. Fix data model or use correct command for key type.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• hget · unhandled-promise-rejection

  error
  WhenCommand promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning
  Required handlingCaller MUST use try-catch or .catch() on all Redis commands.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[3]
• hset · wrong-type-error

  error
  WhenKey exists but is not a hash
  ThrowsReplyError with message containing 'WRONGTYPE'
  Required handlingCaller MUST catch WRONGTYPE errors. Key exists with different type - DO NOT retry.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• hset · unhandled-promise-rejection

  error
  WhenCommand promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning
  Required handlingCaller MUST use try-catch or .catch() on all Redis commands.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[3]
• hgetall · wrong-type-error

  error
  WhenKey exists but is not a hash
  ThrowsReplyError with message containing 'WRONGTYPE'
  Required handlingCaller MUST catch WRONGTYPE errors. Key is not a hash - DO NOT retry.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• hgetall · unhandled-promise-rejection

  error
  WhenCommand promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning
  Required handlingCaller MUST use try-catch or .catch() on all Redis commands.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[3]
• lpush · wrong-type-error

  error
  WhenKey exists but is not a list
  ThrowsReplyError with message containing 'WRONGTYPE'
  Required handlingCaller MUST catch WRONGTYPE errors. Key exists with different type - DO NOT retry.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• lpush · unhandled-promise-rejection

  error
  WhenCommand promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning
  Required handlingCaller MUST use try-catch or .catch() on all Redis commands.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[3]
• rpush · wrong-type-error

  error
  WhenKey exists but is not a list
  ThrowsReplyError with message containing 'WRONGTYPE'
  Required handlingCaller MUST catch WRONGTYPE errors. Key exists with different type - DO NOT retry.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• rpush · unhandled-promise-rejection

  error
  WhenCommand promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning
  Required handlingCaller MUST use try-catch or .catch() on all Redis commands.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[3]
• publish · publish-error

  error
  WhenPublish fails (connection lost, etc.)
  ThrowsNetwork error or UnhandledPromiseRejectionWarning
  Required handlingCaller MUST catch publish errors with try-catch or .catch(). Network errors may be transient - implement retry logic. Returns number of subscribers that received the message (may be 0).
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[13]
• eval · script-error

  error
  WhenLua script has syntax or runtime error
  ThrowsReplyError with script error details
  Required handlingCaller MUST catch Lua script errors. Script syntax errors should NOT be retried - fix script. Script runtime errors depend on logic - may or may not be retriable.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• eval · script-timeout

  error
  WhenLua script exceeds execution time limit
  ThrowsReplyError with timeout message
  Required handlingCaller MUST catch script timeout errors. Redis has lua-time-limit configuration (default 5 seconds). Optimize script or increase limit if needed. DO NOT retry immediately - may cause cascading timeouts.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• quit · quit-promise-unhandled

  error
  Whenquit() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning if connection already closed or network error
  Required handlingCaller MUST use try-catch or .catch() on quit(). quit() sends QUIT to server and waits for pending commands to complete. May reject if connection is already closed or broken before quit completes. Use disconnect() for immediate close if quit() is not available.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[14]
• quit · quit-pending-commands-lost

  warning
  Whenquit() called while commands are still queued
  ThrowsAbortError for queued commands that won't be executed
  Required handlingCaller MUST be aware that quit() waits for pending replies but new commands added after quit() is called will receive AbortError. Do not enqueue commands after calling quit(). Pattern: await all pending operations before calling quit() in shutdown handlers.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[15]
• del · del-unhandled-promise-rejection

  error
  Whendel() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error
  Required handlingCaller MUST use try-catch or .catch() on del() calls. del() returns the count of deleted keys (0 if key doesn't exist — not an error). Returns Promise<number> — check return value only if you need to verify deletion.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• expire · expire-unhandled-promise-rejection

  error
  Whenexpire() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error
  Required handlingCaller MUST use try-catch or .catch() on expire() calls. expire() returns 1 if timeout was set, 0 if key doesn't exist — 0 is NOT an error. Silent expiry failures leave data in Redis indefinitely, causing memory leaks and stale data bugs in session management and rate limiting.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• expire · expire-returns-zero-not-checked

  warning
  Whenexpire() called on non-existent key and return value not checked
  ThrowsN/A (returns 0, not an error)
  Required handlingCaller SHOULD check expire() return value when setting TTL on critical keys. Returns 0 if key does not exist — the set+expire pattern can fail silently if the key was never written or was already deleted between set() and expire() calls. Use SET with EX option (atomic) instead of separate set()+expire() calls: `redis.set(key, value, 'EX', ttlSeconds)` to avoid the race condition.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[16]
• incr · incr-wrong-type-error

  error
  WhenKey exists but is not a string or integer
  ThrowsReplyError with 'ERR value is not an integer or out of range'
  Required handlingCaller MUST catch WRONGTYPE/value-not-integer errors. Happens when key holds a non-integer string (e.g., JSON blob) and incr() is called. This is a programming error — do NOT retry. Fix the data model.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[17]
• incr · incr-unhandled-promise-rejection

  error
  Whenincr() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error
  Required handlingCaller MUST use try-catch or .catch() on incr() calls. Silent incr failures cause rate limiters to fail open (no limiting applied), which can lead to abuse, quota overruns, and billing errors.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• decr · decr-wrong-type-error

  error
  WhenKey exists but is not an integer, or decrement would go below -9223372036854775808
  ThrowsReplyError with 'ERR value is not an integer or out of range'
  Required handlingCaller MUST catch value-not-integer and overflow errors. Overflow at 64-bit integer minimum causes ReplyError — not silent wrap-around. Fix data model or use DECRBY with range validation.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[18]
• decr · decr-unhandled-promise-rejection

  error
  Whendecr() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error
  Required handlingCaller MUST use try-catch or .catch() on decr() calls.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• zadd · zadd-wrong-type-error

  error
  WhenKey exists but is not a sorted set
  ThrowsReplyError with 'WRONGTYPE Operation against a key holding the wrong kind of value'
  Required handlingCaller MUST catch WRONGTYPE errors for sorted set operations. Key exists with different type — DO NOT retry. Fix data model.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• zadd · zadd-nan-score-error

  error
  WhenScore value is NaN
  ThrowsReplyError with 'not a float'
  Required handlingCaller MUST validate score before calling zadd(). NaN scores cause immediate ReplyError. Common when score comes from user input, division operations, or Date arithmetic. Validate: if (isNaN(score) || !isFinite(score)) throw before zadd().
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[19]
• zadd · zadd-unhandled-promise-rejection

  error
  Whenzadd() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error
  Required handlingCaller MUST use try-catch or .catch() on zadd() calls.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• zrange · zrange-wrong-type-error

  error
  WhenKey exists but is not a sorted set
  ThrowsReplyError with 'WRONGTYPE Operation against a key holding the wrong kind of value'
  Required handlingCaller MUST catch WRONGTYPE errors. Key is not a sorted set — DO NOT retry. Fix data model.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• zrange · zrange-unhandled-promise-rejection

  error
  Whenzrange() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error
  Required handlingCaller MUST use try-catch or .catch() on zrange() calls. Returns empty array if key doesn't exist — not an error.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• zrem · zrem-wrong-type-error

  error
  WhenKey exists but is not a sorted set
  ThrowsReplyError with 'WRONGTYPE Operation against a key holding the wrong kind of value'
  Required handlingCaller MUST catch WRONGTYPE errors. Returns 0 if member doesn't exist (not an error).
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• zrem · zrem-unhandled-promise-rejection

  error
  Whenzrem() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error
  Required handlingCaller MUST use try-catch or .catch() on zrem() calls.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• sadd · sadd-wrong-type-error

  error
  WhenKey exists but is not a set
  ThrowsReplyError with 'WRONGTYPE Operation against a key holding the wrong kind of value'
  Required handlingCaller MUST catch WRONGTYPE errors for set operations. Key exists with different type — DO NOT retry. Fix data model.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• sadd · sadd-unhandled-promise-rejection

  error
  Whensadd() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error
  Required handlingCaller MUST use try-catch or .catch() on sadd() calls. Returns count of new members added (0 if already in set — not an error).
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• smembers · smembers-wrong-type-error

  error
  WhenKey exists but is not a set
  ThrowsReplyError with 'WRONGTYPE Operation against a key holding the wrong kind of value'
  Required handlingCaller MUST catch WRONGTYPE errors. Returns empty array if key doesn't exist — not an error. For large sets, consider SSCAN instead to avoid blocking Redis.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• smembers · smembers-large-set-blocking

  warning
  WhenSet has thousands of members and smembers() is called in production
  ThrowsN/A — but Redis blocks for the duration, causing latency for all other clients
  Required handlingCaller SHOULD use sscanStream() for large sets instead of smembers(). smembers() returns ALL members in one blocking call. For sets > 1000 members, use cursor-based sscan() to avoid blocking Redis.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[20]
• smembers · smembers-unhandled-promise-rejection

  error
  Whensmembers() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error
  Required handlingCaller MUST use try-catch or .catch() on smembers() calls.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• srem · srem-wrong-type-error

  error
  WhenKey exists but is not a set
  ThrowsReplyError with 'WRONGTYPE Operation against a key holding the wrong kind of value'
  Required handlingCaller MUST catch WRONGTYPE errors. Returns 0 if member doesn't exist (not an error).
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• srem · srem-unhandled-promise-rejection

  error
  Whensrem() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error
  Required handlingCaller MUST use try-catch or .catch() on srem() calls.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• blpop · blpop-blocking-without-timeout

  warning
  Whenblpop() called without timeout parameter or with timeout=0
  ThrowsCommand may block indefinitely, causing resource exhaustion
  Required handlingCaller SHOULD always provide a non-zero timeout to blpop(). With timeout=0, command blocks until data is available — may be indefinite. In SaaS apps, this can exhaust connection pool and cause other commands to queue. Recommended: use a reasonable timeout (5-30 seconds) and loop to re-poll. Pattern: while (running) { const result = await redis.blpop('queue', 5); ... }
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[21]
• blpop · blpop-unhandled-promise-rejection

  error
  Whenblpop() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error or MaxRetriesPerRequestError
  Required handlingCaller MUST use try-catch or .catch() on blpop() calls. Connection errors during blocking commands return MaxRetriesPerRequestError. Implement retry loop with backoff for job queue consumers.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12]
• blpop · blpop-subscriber-mode-conflict

  error
  Whenblpop() called on a connection in subscriber mode
  ThrowsReplyError: Connection in subscriber mode, only subscriber commands allowed
  Required handlingCaller MUST NOT mix blpop() with pub/sub subscriptions on the same connection. Use a dedicated connection (redis.duplicate()) for job queue operations.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[9]
• exec · exec-results-not-checked

  error
  Whenexec() returned array but individual [error, result] tuples are not inspected
  ThrowsPer-command errors are silently embedded in the result array, NOT thrown by the outer Promise
  Required handlingCaller MUST iterate exec()'s return value and check each [error, result] tuple. Format: `[[null, 'OK'], [Error, undefined], [null, 42], ...]`. The outer Promise resolves successfully even when individual commands fail — the failures are hidden in the array. Skipping the per-tuple check silently drops failed writes (cache invalidation, rate-limit increments, job-enqueue) and leaves the application thinking the transaction succeeded. Pattern: const results = await tx.exec(); for (const [err, _] of results ?? []) if (err) handle(err);
  costmediumin prodsilent failureusers seelost datavisibilitysilent
  Sources[22][12]
• exec · exec-null-return-not-checked

  error
  Whenexec() returns null after WATCH and return value is not checked
  ThrowsN/A — null is the success-but-aborted signal, not an error
  Required handlingCaller MUST check whether exec() returned null when WATCH was used. Null indicates a watched key was modified between WATCH and EXEC, so the transaction was discarded and NONE of the queued commands ran. Treating null as success corrupts optimistic-concurrency patterns (inventory decrement, balance updates, leader election) by silently dropping the retry that the WATCH/MULTI/EXEC pattern depends on. Pattern: const results = await tx.exec(); if (results === null) return retry();
  costmediumin prodsilent failureusers seelost datavisibilitysilent
  Sources[23][7]
• exec · exec-unhandled-promise-rejection

  error
  Whenexec() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error or EXECABORT
  Required handlingCaller MUST use try-catch or .catch() on tx.exec() / pipeline.exec(). The outer Promise CAN reject (separately from per-command errors) when the connection drops mid-EXEC or when EXECABORT fires because a queued command failed validation (WRONGTYPE on a queued op, queueing-time syntax errors). Unhandled rejection leaves the transaction in an unknown state — neither caller nor caller's caller knows whether the writes landed.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[12][8]
• exists · exists-unhandled-promise-rejection

  error
  Whenexists() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error
  Required handlingCaller MUST use try-catch or .catch() on exists() calls. A rejected exists() that the application reads as 'key missing' fails OPEN in idempotency-key and rate-limit code paths: the duplicate request gets processed, the throttle is bypassed. This is one of the highest-impact silent-failure modes in SaaS — connection blip during an idempotency probe lets the same Stripe charge fire twice. Pattern: never let a rejected probe be coerced into 'not present'.
  costhighin prodsilent failureusers seelost datavisibilitysilent
  Sources[24][12]
• exists · exists-return-coerced-to-boolean-without-zero-check

  warning
  Whenexists() result is used in a truthy/falsy boolean check rather than compared to a specific count
  ThrowsN/A — JavaScript coercion bug, not a Redis-thrown error
  Required handlingCaller SHOULD compare exists() return value to a specific number, not coerce to boolean. exists() returns a NUMBER, not a boolean. For multi-key probes (`exists(a, b, c)` returns 0, 1, 2, or 3), a truthy check `if (await redis.exists(a, b, c))` flags as 'all present' even when only 1 of 3 exists — a common bug in cache-aside patterns that require all keys to be present. Pattern: if ((await redis.exists(a, b, c)) === 3) usePopulatedCache();
  costlowin prodsilent failureusers seelost datavisibilitysilent
  Sources[24]
• getex · getex-wrong-type-error

  error
  WhenKey exists but holds a non-string value (hash, list, set, sorted set, stream)
  ThrowsReplyError with 'WRONGTYPE Operation against a key holding the wrong kind of value'
  Required handlingCaller MUST catch WRONGTYPE errors on getex(). Like GET, getex() is a string-only command — calling it on a hash or list throws WRONGTYPE. This is a programming error: fix the data model or use the correct command for the actual key type. Do NOT retry — the type mismatch is deterministic.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[25][12]
• getex · getex-unhandled-promise-rejection

  error
  Whengetex() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error or server <6.2
  Required handlingCaller MUST use try-catch or .catch() on getex() calls. getex() rejects on the usual connection errors (ECONNREFUSED, ETIMEDOUT, ECONNRESET) AND on 'ERR unknown command' if the connected Redis server is older than 6.2.0 — easy regression mode when an env points at a legacy Redis 6.0/6.1 instance. Without a catch, the session-refresh silently dies and the user gets logged out unexpectedly.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[25][12]
• getex · getex-invalid-ttl-arguments

  error
  WhenEX/PX/EXAT/PXAT argument is negative, zero, NaN, or non-finite
  ThrowsReplyError with 'ERR invalid expire time in 'getex' command'
  Required handlingCaller MUST validate TTL arguments before passing to getex(). Negative seconds, NaN from Date arithmetic, or 0 cause immediate ReplyError. Common when the TTL is computed from `expiresAt - Date.now()` and the timestamp already elapsed — the rejected promise breaks session-refresh in a way that's hard to trace. Pattern: clamp/validate before call, or use PERSIST to clear TTL.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[25]
• getdel · getdel-wrong-type-error

  error
  WhenKey exists but holds a non-string value
  ThrowsReplyError with 'WRONGTYPE Operation against a key holding the wrong kind of value'
  Required handlingCaller MUST catch WRONGTYPE errors on getdel(). Like GET and GETEX, getdel() is string-only — calling it on a hash, list, set, or sorted set throws WRONGTYPE. Do NOT retry. Fix the data model or use the correct command (HDEL/SPOP/LPOP) for the actual key type.
  costmediumin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[26][12]
• getdel · getdel-unhandled-promise-rejection

  error
  Whengetdel() promise rejected without catch handler
  ThrowsUnhandledPromiseRejectionWarning on connection error or server <6.2
  Required handlingCaller MUST use try-catch or .catch() on getdel() calls. Rejects on connection errors and on 'ERR unknown command' for Redis servers older than 6.2.0. Silent rejection in a one-time-token flow leaves the token in Redis (because the DELETE side never ran) AND returns undefined to the caller — the user sees "invalid token" but the token is still valid, blocking subsequent legitimate attempts. For magic-link flows this manifests as users unable to complete login after a transient Redis hiccup.
  costhighin prodimmediate exceptionusers seeservice unavailablevisibilityvisible
  Sources[26][12]
• getdel · getdel-null-return-not-distinguished-from-error

  warning
  Whengetdel() returns null and the application treats null as 'consumed by another worker' without distinguishing from connection failure
  ThrowsN/A — null is the documented 'key did not exist' return; error case is a thrown rejection
  Required handlingCaller SHOULD log/metric the null-return case separately from the rejection case in token-consumption flows. A null return means 'key was never set OR was already consumed' — a legitimate outcome. A rejection means 'we don't know whether the key was consumed' — an ambiguous failure that needs operator visibility. Conflating them in logs (`if (!token) reject('invalid')`) hides connection issues behind a flood of legitimate-looking 'invalid token' errors.
  costlowin prodsilent failureusers seelost datavisibilitysilent
  Sources[26]

Sources

Every postcondition cites at least one of these. Grouped by source type; numbered to match the footnotes above.

Research notes

Curator notes from SOURCES.md captured when the profile was written so you can verify the reasoning, not just the rules.

// ❌ WRONG - Errors silently logged to console
const redis = new Redis();

// ✅ REQUIRED - Explicit error listener
const redis = new Redis();
redis.on('error', (err) => {
  logger.error('Redis connection error:', err);
});

const results = await pipeline.exec();
// Check each result: results[0][0] is error, results[0][1] is value

await redis.watch('key');
// ... key modified by another client ...
const result = await redis.multi().set('key', 'value').exec();
if (result === null) {
  // Transaction aborted due to WATCH violation
}

await redis.subscribe('channel');
await redis.get('key'); // ❌ Error: Connection in subscriber mode