What are the HSK chengyu (idioms)? I've been going through the HSK lists with awk, so I now feel like I can answer...

Question: What are the HSK chengyu (idioms)?

My answer is below.

To my knowledge, there's no HSK5 idioms, except possibly 讨价还价 (to haggle over price), but I don't think that counts.  This is not to say there's no requirement to learn idioms for HSK5, but that it's not on the official list.
HSK6 idioms (from vocab list).  English definitions from CC-CEDICT.



  一丝不苟 (yīsībùgǒu)not one thread loose (idiom); strictly according to the rulesBaike; Jukuu; Yabla


  一举两得 (yījǔliǎngdé)one move, two gains (idiom); two birds with one stoneBaike; Jukuu; Yabla


  一如既往 (yīrújìwǎng)just as in the past (idiom); as beforeBaike; Jukuu; Yabla


  一帆风顺 (yīfānfēngshùn)propitious wind throughout the journey (idiom)Baike; Jukuu; Yabla


  一目了然 (yīmùliǎorán)obvious at a glance (idiom)Baike; Jukuu; Yabla


  不可思议 (bùkěsīyì)inconceivable (idiom); unimaginableBaike; Jukuu; Yabla


  不屑一顾 (bùxièyīgù)to disdain as beneath contempt (idiom)Baike; Jukuu; Yabla


  不择手段 (bùzéshǒuduàn)by fair means or foulBaike; Jukuu; Yabla


  不相上下 (bùxiāngshàngxià)equally matchedBaike; Jukuu; Yabla


  不言而喻 (bùyánéryù)it goes without sayingBaike; Jukuu; Yabla


  与日俱增 (yǔrìjùzēng)to increase steadilyBaike; Jukuu; Yabla


  东张西望 (dōngzhāngxīwàng)to look in all directions (idiom)Baike; Jukuu; Yabla


  丢三落四 (diūsānlàsì)forgetfulBaike; Jukuu; Yabla


  举世瞩目 (jǔshìzhǔmù)to receive worldwide attentionBaike; Jukuu; Yabla


  举足轻重 (jǔzúqīngzhòng)to play a critical role (idiom)Baike; Jukuu; Yabla


  争先恐后 (zhēngxiānkǒnghòu)striving to be first and fearing to be last (idiom); outdoing one anotherBaike; Jukuu; Yabla


  任重道远 (rènzhòngdàoyuǎn)a heavy load and a long roadBaike; Jukuu; Yabla


  众所周知 (zhòngsuǒzhōuzhī)as everyone knows (idiom)Baike; Jukuu; Yabla


  优胜劣汰 (yōushèngliètài)survival of the fittest (idiom)Baike; Jukuu; Yabla


  侃侃而谈 (kǎnkǎnértán)to speak frankly with assuranceBaike; Jukuu; Yabla


  供不应求 (gōngbùyìngqiú)supply does not meet demandBaike; Jukuu; Yabla


  兢兢业业 (jīngjīngyèyè)cautious and conscientiousBaike; Jukuu; Yabla


  全力以赴 (quánlìyǐfù)to do at all costsBaike; Jukuu; Yabla


  兴致勃勃 (xìngzhìbóbó)to become exhilarated (idiom); in high spiritsBaike; Jukuu; Yabla


  兴高采烈 (xìnggāocǎiliè)happy and excited (idiom)Baike; Jukuu; Yabla


  再接再厉 (zàijiēzàilì)to continue the struggle (idiom); to persistBaike; Jukuu; Yabla


  刻不容缓 (kèbùrónghuǎn)to brook no delayBaike; Jukuu; Yabla


  力所能及 (lìsuǒnéngjí)as far as one's capabilities extend (idiom); to the best of one's abilityBaike; Jukuu; Yabla


  千方百计 (qiānfāngbǎijì)lit. thousand ways, a hundred plans (idiom); by every possible meansBaike; Jukuu; Yabla


  半途而废 (bàntú'érfèi)to give up halfway (idiom); leave sth unfinishedBaike; Jukuu; Yabla


  南辕北辙 (nányuánběizhé)to act in a way that defeats one's purpose (idiom)Baike; Jukuu; Yabla


  博大精深 (bódàjīngshēn)wide-ranging and profoundBaike; Jukuu; Yabla


  各抒己见 (gèshūjǐjiàn)everyone gives their own viewBaike; Jukuu; Yabla


  名副其实 (míngfùqíshí)not just in name only, but also in reality (idiom)Baike; Jukuu; Yabla


  后顾之忧 (hòugùzhīyōu)fears of trouble in the rear (idiom); family worries (obstructing freedom of action)Baike; Jukuu; Yabla


  吞吞吐吐 (tūntūntǔtǔ)to hum and haw (idiom); to mumble as if hiding sthBaike; Jukuu; Yabla


  喜闻乐见 (xǐwénlèjiàn)to love to hear and see (idiom)Baike; Jukuu; Yabla


  天伦之乐 (tiānlúnzhīlè)family love and joyBaike; Jukuu; Yabla


  实事求是 (shíshìqiúshì)to seek truth from facts (idiom)Baike; Jukuu; Yabla


  家喻户晓 (jiāyùhùxiǎo)understood by everyone (idiom); well knownBaike; Jukuu; Yabla


  小心翼翼 (xiǎoxīnyìyì)cautious and solemn (idiom); very carefullyBaike; Jukuu; Yabla


  层出不穷 (céngchūbùqióng)more and more emergeBaike; Jukuu; Yabla


  岂有此理 (qǐyǒucǐlǐ)how can this be so? (idiom); preposterousBaike; Jukuu; Yabla


  川流不息 (chuānliúbùxī)the stream flows without stopping (idiom); unending flowBaike; Jukuu; Yabla


  废寝忘食 (fèiqǐnwàngshí)to neglect sleep and forget about food (idiom)Baike; Jukuu; Yabla


  归根到底 (guīgēndàodǐ)after allBaike; Jukuu; Yabla


  当务之急 (dāngwùzhījí)top priority jobBaike; Jukuu; Yabla


  得不偿失 (débùchángshī)the gains do not make up for the losses (idiom)Baike; Jukuu; Yabla


  得天独厚 (détiāndúhòu)blessed by heaven (idiom)Baike; Jukuu; Yabla


  循序渐进 (xúnxùjiànjìn)in sequence, step by step (idiom); to make steady progress incrementallyBaike; Jukuu; Yabla


  心甘情愿 (xīngānqíngyuàn)delighted to (do sth, idiom)Baike; Jukuu; Yabla


  急于求成 (jíyúqiúchéng)anxious for quick results (idiom)Baike; Jukuu; Yabla


  急功近利 (jígōngjìnlì)seeking instant benefit (idiom); shortsighted vision, looking only for fast returnBaike; Jukuu; Yabla


  总而言之 (zǒng'éryánzhī)in shortBaike; Jukuu; Yabla


  恍然大悟 (huǎngrándàwù)to suddenly realizeBaike; Jukuu; Yabla


  恰到好处 (qiàdàohǎochù)it's just perfectBaike; Jukuu; Yabla


  悬崖峭壁 (xuányáqiàobì)sheer cliffs and precipitous rock faces (idiom)Baike; Jukuu; Yabla


  想方设法 (xiǎngfāngshèfǎ)to think up every possible method (idiom); to devise ways and meansBaike; Jukuu; Yabla


  拔苗助长 (bámiáozhùzhǎng)to spoil things through excessive enthusiasm (idiom)Baike; Jukuu; Yabla


  斩钉截铁 (zhǎndīngjiétiě)lit. to chop the nail and slice the iron (idiom)Baike; Jukuu; Yabla


  新陈代谢 (xīnchéndàixiè)metabolism (biology); the new replaces the old (idiom)Baike; Jukuu; Yabla


  无动于衷 (wúdòngyúzhōng)aloofBaike; Jukuu; Yabla


  无微不至 (wúwēibùzhì)in every possible way (idiom); meticulousBaike; Jukuu; Yabla


  无忧无虑 (wúyōuwúlǜ)carefree and without worries (idiom)Baike; Jukuu; Yabla


  无理取闹 (wúlǐqǔnào)to make trouble without reason (idiom); to be deliberately provocativeBaike; Jukuu; Yabla


  无穷无尽 (wúqióngwújìn)endlessBaike; Jukuu; Yabla


  无精打采 (wújīngdǎcǎi)dispirited and downcast (idiom); listlessBaike; Jukuu; Yabla


  无能为力 (wúnéngwéilì)impotent (idiom)Baike; Jukuu; Yabla


  日新月异 (rìxīnyuèyì)daily renewal, monthly change (idiom)Baike; Jukuu; Yabla


  有条不紊 (yǒutiáobùwěn)regular and thorough (idiom); methodically arrangedBaike; Jukuu; Yabla


  朝气蓬勃 (zhāoqìpéngbó)full of youthful energy (idiom); vigorousBaike; Jukuu; Yabla


  根深蒂固 (gēnshēndìgù)deep-rooted (problem etc)Baike; Jukuu; Yabla


  欣欣向荣 (xīnxīnxiàngróng)(idiom) flourishingBaike; Jukuu; Yabla


  津津有味 (jīnjīnyǒuwèi)with keen interest pleasure (idiom); with gustoBaike; Jukuu; Yabla


  深情厚谊 (shēnqínghòuyì)deep friendshipBaike; Jukuu; Yabla


  滔滔不绝 (tāotāobùjué)unceasing torrent (idiom)Baike; Jukuu; Yabla


  潜移默化 (qiányímòhuà)imperceptible influenceBaike; Jukuu; Yabla


  热泪盈眶 (rèlèiyíngkuàng)eyes brimming with tears of excitement (idiom)Baike; Jukuu; Yabla


  爱不释手 (àibùshìshǒu)to love sth too much to part with it (idiom); to fondle admiringlyBaike; Jukuu; Yabla


  物美价廉 (wùměijiàlián)good quality and cheapBaike; Jukuu; Yabla


  狼吞虎咽 (lángtūnhǔyàn)to wolf down one's food (idiom); to devour ravenouslyBaike; Jukuu; Yabla


  理所当然 (lǐsuǒdāngrán)as it should be by rights (idiom)Baike; Jukuu; Yabla


  理直气壮 (lǐzhíqìzhuàng)in the right and self-confident (idiom)Baike; Jukuu; Yabla


  画蛇添足 (huàshétiānzú)lit. draw legs on a snake (idiom); fig. to ruin the effect by adding sth superfluousBaike; Jukuu; Yabla


  相辅相成 (xiāngfǔxiāngchéng)to complement one another (idiom)Baike; Jukuu; Yabla


  知足常乐 (zhīzúchánglè)satisfied with what one has (idiom)Baike; Jukuu; Yabla


  礼尚往来 (lǐshàngwǎnglái)lit. proper behavior is based on reciprocity (idiom)Baike; Jukuu; Yabla


  称心如意 (chènxīnrúyì)after one's heart (idiom); gratifying and satisfactoryBaike; Jukuu; Yabla


  空前绝后 (kōngqiánjuéhòu)unprecedented and never to be duplicatedBaike; Jukuu; Yabla


  竭尽全力 (jiéjìnquánlì)to spare no effort (idiom); to do one's utmostBaike; Jukuu; Yabla


  精打细算 (jīngdǎxìsuàn)meticulous planning and careful accounting (idiom)Baike; Jukuu; Yabla


  精益求精 (jīngyìqiújīng)to perfect sth that is already outstanding (idiom); constantly improvingBaike; Jukuu; Yabla


  络绎不绝 (luòyìbùjué)continuously; in an endless stream (idiom)Baike; Jukuu; Yabla


  统筹兼顾 (tǒngchóujiāngù)an overall plan taking into account all factorsBaike; Jukuu; Yabla


  聚精会神 (jùjīnghuìshén)to concentrate one's attention (idiom)Baike; Jukuu; Yabla


  肆无忌惮 (sìwújìdàn)absolutely unrestrainedBaike; Jukuu; Yabla


  自力更生 (zìlìgēngshēng)regeneration through one's own effort (idiom)Baike; Jukuu; Yabla


  苦尽甘来 (kǔjìngānlái)bitterness finishes, sweetness begins (idiom); the hard times are over, the good times just beginningBaike; Jukuu; Yabla


  莫名其妙 (mòmíngqímiào)(idiom) bafflingBaike; Jukuu; Yabla


  见义勇为 (jiànyìyǒngwéi)to see what is right and act courageously (idiom, from Analects)Baike; Jukuu; Yabla


  见多识广 (jiànduōshìguǎng)experienced and knowledgeable (idiom)Baike; Jukuu; Yabla


  迄今为止 (qìjīnwéizhǐ)so farBaike; Jukuu; Yabla


  迫不及待 (pòbùjídài)impatient (idiom); in a hurryBaike; Jukuu; Yabla


  锦上添花 (jǐnshàngtiānhuā)lit. on brocade, add flowers (idiom); to decorate sth already perfectBaike; Jukuu; Yabla


  锲而不舍 (qiè'érbùshě)to chip away at a task and not abandon it (idiom); to chisel away at sthBaike; Jukuu; Yabla


  难能可贵 (nánnéngkěguì)rare and preciousBaike; Jukuu; Yabla


  雪上加霜 (xuěshàngjiāshuāng)to add hail to snow (idiom); one disaster on top of anotherBaike; Jukuu; Yabla


  风土人情 (fēngtǔrénqíng)local conditions and customs (idiom)Baike; Jukuu; Yabla


  饱经沧桑 (bǎojīngcāngsāng)having lived through many changesBaike; Jukuu; Yabla


  鸦雀无声 (yāquèwúshēng)lit. crow and peacock make no sound; absolute silence (idiom)Baike; Jukuu; Yabla


  齐心协力 (qíxīnxiélì)to work with a common purpose (idiom); to make concerted effortsBaike; Jukuu; Yabla



Not counted: 二氧化碳 (carbon dioxide), 公共汽车 (bus), 名胜古迹 (historical sites), 微不足道 (negligible), 烟花爆竹 (firecrackers), 电子邮件 (email), 高速公路 (expressway), 通货膨胀 (inflation), 飞禽走兽 (birds and animals), 讨价还价 (haggle over price).