You've probably read that when you encounter a ーいる or ーえる verb, it's probably ichidan, but might be godan. This is true -- there are a couple thousand ichidan verbs and only a few hundred ーいる or ーえる godan verbs, including compounds. But there's actually a more sure-fire way to guess at the conjugation, if the kanji form of the verb is handy.
The hiragana end of the verb which is inflected is called okurigana. Standard okurigana usage calls for the okurigana to start with the first inflected mora. In godan ーいる or ーえる verbs, this is る. But with ichidan verbs, the first inflected mora is considered to be the ーい or ーえ mora, even though that mora itself never changes. One way to think of this is that there's usually one okurigana between the kanji verb stem and ます when in ます form, or ない when in ない form.
For example, the godan verb 切る will always contain a hiragana from the ら row: 切らない, 切ります. The ichidan verb 食べる always has べ: 食べない, 食べます.
In other words godan verbs which are ーいる or ーえる will usually end with a kanji followed immediately by る, while ichidan verbs will usually end with two or more hiragana. There are very few exceptions to these guidelines, usually because the kanji of godan verbs has turned to hiragana, or because an ichidan verb is only two mora long (so there's not enough "room" for a kanji and two hiragana).
Exceptions from edict:
出る [でる] /(v1) to appear/to come forth/to leave/(P)/ In many compounds
見る [みる] /(v1) to see/to watch/(P)/ In many compounds
看る [みる] /(oK) (v1) to look after/to take care of/(P)/ Related to 見る
診る [みる] /(v1) to examine (medical)/(P)/ Related to 見る
観る [みる] /(oK) (v1) to view (i.e. flowers, movie)/ Related to 見る
居る [いる] /(v1) (uk) (hum) to be (animate)/to exist/(P)/ In some compounds
獲る/得る [える] /(v1) to get/to gain/to win/(P)/ In some compounds
似る [にる] /(v1) to resemble/to be similar/(P)/
真似る [まねる] /(v1) to mimic/to imitate/(P)/
寝る [ねる] /(v1) to go to bed/to lie down/to sleep/(P)/
鑄る/鋳る [いる] /(v1) to cast/to mint/to coin/(P)/
悄気る [しょげる] /(v1) to be dispirited/to be dejected/to be disheartened/to lose heart/
惚気る [のろける] /(v1) to play up/to speak fondly of/to praise one's spouse/
干る [ひる] /(v1) to dry/(P)/
着る [きる] /(v1) to wear/to put on (from shoulders down)/(P)/
経る [へる] /(v1) to pass/to elapse/to experience/(P)/
射る [いる] /(v1) to shoot/(P)/
煮る [にる] /(v1,vt) to boil/to cook/(P)/
洒落る [しゃれる] /(v1) to joke/to play on words/to dress stylishly/(P)/
魂消る [たまげる] /(v1) to be astonished/to be startled/to be appalled/
道化る [どうける] /(v1) to jest/to clown (around)/
悪擦る [わるずれる] /(v1) to get worse and worse/
出来る [できる] /(uk) (v1) to be able to/to be ready/to occur/(P)/
時化る [しける] /(uk) (v1) to be stormy or choppy (sea)/to go through hard times/
不山戯る [ふざける] /(uk) (iK) (v1) to romp/to gambol/to frolic/to joke/to make fun of/to flirt/(P)/
巫山戯る [ふざける] /(uk) (v1) to romp/to gambol/to frolic/to joke/to make fun of/to flirt/
下卑る [げびる] /(v1) to become vulgar/to coarsen/ Usually 下びる
痩る/瘠る [やせる] /(io) (v1) to become thin/to lose weight/to reduce (one's) weight/to slim/
詫る [わびる] /(io) (v1) to apologize/
吠る [ほえる] /(io) (v1) to bark/to bay/to howl/to bellow/to roar/to cry/
落る [おちる] /(io) (v1) (1) to fall down/to drop/(2) to fail (e.g. exam)/(3) to crash/to degenerate/to degrade/
佗る [わびる] /(io) (v1) to be worried/to be grieved/to pine for/
黴る [かびる] /(io) (v1) to become moldy or musty/
倦る [あきる] /(io) (v1) to get tired of/to lose interest in/to have enough/
見附る [みつける] /(io) (v1) to be familiar/to discover/to find fault/to detect/to find out/to locate/
仕向る [しむける] /(io) (v1) to induce/to tempt/to treat/to act toward/to handle (men)/to send/to forward to/
引付る [ひきつける] /(io) (v1) to fascinate/to pull up (at a gate)/to have a convulsion/to attract/
割付る [わりつける] /(io) (v1) to allot/to distribute/to lay out/to divide among/to assign/
腰掛る [こしかける] /(io) (v1) to sit (down)/
引受る [ひきうける] /(io) (v1) to undertake/to take up/to take over/to be responsible for/to guarantee
/to contract (disease)
引替る [ひきかえる] /(io) (v1) to exchange (things)/to reverse/
引当る [ひきあてる] /(io) (v1) to apply/to compare/
取換る [とりかえる] /(io) (v1) to exchange/to replace/
畝ねる [うねる] /(v5r) to undulate/to meander/to surge/to swell/to roll/to wind/(P)
捩じる [ねじる] /(v5r) (1) to screw/to twist/(2) to distort/(3) to torture/to wrest/(P)
交じる [まじる] /(v5r,vi) to be mixed/to be blended with/to associate with/to mingle with/to interest
/to join/(P)/ In few compounds
混じる [まじる] /(v5r,vi) to be mixed/to be blended with/to associate with/to mingle with/to interest
/to join/(P)/
しくじる [しくじる] /(v5r) to fail/to fall through/to blunder/(P)/
拗じる [ねじる] /(v5r) (1) to screw/to twist/(2) to distort/(3) to torture/to wrest/
捻じる [ねじる] /(v5r) (1) to screw/to twist/(2) to distort/(3) to torture/to wrest/
いびる [いびる] /(v5r) to tease/
くねる [くねる] /(v5r,vi) to bend loosely back and forth/
せびる [せびる] /(v5r) to demand money/to pester/to extort/
のめる [のめる] /(v5r) to fall/
アジる [アジる] /(v5r) to stir up/to instigate (somebody to do something)/
デニる [デニる] /(v5r) to eat at Denny's/
臥せる [ふせる] /(v5r) to lie down/to retire/to go to bed/
寝そべる [ねそべる] /(v5r) to sprawl/to lie sprawled/
褒めちぎる [ほめちぎる] /(v5r) to praise (to the skies)/to sing the praises (of)/to extol/
誉めちぎる [ほめちぎる] /(v5r) to praise (to the skies)/to sing the praises (of)/to extol/
曲りくねる [まがりくねる] /(v5r,vi) to bend many times/to turn and twist/to zigzag/
曲がりくねる [まがりくねる] /(v5r,vi) to bend many times/to turn and twist/to zigzag/
つんのめる [つんのめる] /(v5r) to pitch (fall) forward/
引きちぎる [ひきちぎる] /(v5r) to tear off/
嘲る [あざける] /(v5r) (uk) to scoff/(P)/
漲る [みなぎる] /(v5r) (uk) to swell up/to rise/to be (brim) full of/to pervade/
迸る [ほとばしる] /(io) (v5r) (uk) to surge/to well up/to gush out/
吝嗇る [けちる] /(v5r) (uk) to be stingy/to scrimp/
見くびる [みくびる] /(v5r) to underrate/to belittle/to look down on/to despise/ Usually 見縊る
突っきる [つっきる] /(v5r) to cross/to go across/to go through/to cut across/ Usually 突っ切る
降りしきる [ふりしきる] /(v5r) to rain incessantly/to downpour/ From 降り頻る
読み耽ける [よみふける] /(io) (v5r) to be absorbed in reading/
雑じる [まじる] /(io) (v5r) to mix/
阿ねる [おもねる] /(io) (v5r) to flatter/
耽ける [ふける] /(io) (v5r) to indulge in/to give oneself up to/to be obsessed by/to be engrossed in
/to be lost in/to be absorbed in/
陰げる [かげる] /(io) (v5r) to darken/to get dark/to be clouded/to be obscured/
切る [きる] /(suf,v5r) to cut/to chop/to hash/to carve/to saw/to clip/to shear/to slice/to strip/to fell
/to cut down/to punch/to sever (connections)/to pause/to break off/to disconnect/to turn off
/to hang up/to cross (a street)/to discount/to sell below cost/to shake (water) off/to finish
/to be through/to complete/(P)/
返る [かえる] /(v5r) to return/to come back/to go back/(P)/
帰る [かえる] /(v5r) to go back/to go home/to come home/to return/(P)/
入る [いる] /(v5r) to get in/to go in/to come in/to flow into/to set/to set in/(P)/
入る [はいる] /(v5r) to enter/to break into/to join/to enroll/to contain/to hold/to accommodate
/to have (an income of)/(P)/
走る [はしる] /(v5r) to run/(P)/
Most content on this pages was derived from the Electronic Dictionary Research and Development Group's edict. This is in conformance with the licence.