fastly (quickly)

'Fastly' is not standard in modern English. Use 'quickly' for formal or neutral writing and 'fast' in casual speech. Below are clear rules, many ready-to-copy wrong→right pairs, and rewrite templates for work, school, and everyday use.

Quick answer

Avoid 'fastly.' Use 'quickly' for formal or neutral contexts and 'fast' for informal speech. 'Fastly' reads archaic or like a typo.

Incorrect: "He finished the race fastly."
Formal / safe: "He finished the race quickly."
Casual / spoken: "He finished the race fast."

Core explanation: why 'fastly' feels wrong

'Fast' already works as an adverb today (run fast, drive fast). English once formed 'fastly,' but that form fell out of use. Seeing 'fastly' now usually signals an error or an archaic tone.

Choose a modern adverb instead: 'quickly,' 'rapidly,' or 'promptly' depending on tone and meaning. Reserve 'fast' for informal contexts and idioms where it belongs.

'fast' = adjective or adverb in modern use: "a fast car" / "run fast"
'quickly' = standard adverb for neutral or formal tone
Avoid 'fastly' in professional, academic, or published writing

Grammar note: picking fast / quickly / rapidly

Default to 'quickly' for professional audiences (managers, graders, readers of publications). Use 'rapidly' when you want a slightly more technical or scientific tone. Use 'fast' in conversation, dialogue, or casual notes.

Be careful with idioms: some fixed phrases use 'fast' (hold fast, fast asleep) and should not be changed to 'quickly.'

Formal: "She responded quickly."
Technical: "The reagent reacted rapidly."
Casual: "She responded fast."

Hyphenation & spacing: don't invent forms like 'fast-ly' or 'fast ly'

There is no correct hyphenated or split form of 'fastly.' Writing 'fast-ly' or 'fast ly' only looks like an error. Hyphenation doesn't turn a nonstandard form into a standard one.

If you need emphasis, use 'very fast' (casual) or 'very quickly' (formal), or restructure the sentence: "She finished quickly" → "She finished in record time."

Wrong: 'fast-ly' or 'fast ly'
Better: 'quickly', 'very quickly', 'very fast', or a rephrasing

Small wording fixes that improve tone

Replacing one nonstandard word-'fastly' → 'quickly'-improves clarity and trust. Run a quick search for nonstandard adverbs before finalizing important documents.

Real usage by audience: pick the word that fits

When unsure, 'quickly' is a safe choice. Use 'fast' in dialogue, chats, or informal copy. Keep 'fastly' out of drafts.

Work / professional: 'quickly' or 'promptly' - looks polished
School / academic: 'quickly' or 'rapidly' - clear and standard
Casual / chat / narrative: 'fast' - idiomatic and concise

Try your sentence in context

Test the whole sentence rather than the single word. Context usually makes the best choice obvious.

Examples: ready-to-copy wrong → right pairs (work, school, casual)

Each wrong sentence below uses 'fastly' (incorrect). The right sentence shows the modern replacement you can paste into your draft.

Work - Wrong: "She submitted the report fastly to meet the deadline." -
Right: "She submitted the report quickly to meet the deadline."
Work - Wrong: "Please review the attached draft fastly." -
Right: "Please review the attached draft as soon as possible."
Work - Wrong: "The team completed the rollout fastly." -
Right: "The team completed the rollout quickly."
School - Wrong: "He finished the assignment fastly and turned it in." -
Right: "He finished the assignment quickly and turned it in."
School - Wrong: "The reaction occurred fastly after adding the catalyst." -
Right: "The reaction occurred rapidly after adding the catalyst."
School - Wrong: "She spoke fastly during the presentation." -
Right: "She spoke quickly during the presentation."
Casual - Wrong: "I ran to the bus and got there fastly." -
Right: "I ran to the bus and got there fast."
Casual - Wrong: "We fixed the app bug fastly." -
Right: "We fixed the app bug quickly." (or "We fixed it fast" for chat)
General - Wrong: "The dishwasher finished the cycle fastly." - Right: "The dishwasher finished the cycle quickly."
Idiom note: "He held fast to his opinion." - keep 'fast' in idioms; do not change to 'quickly.'

Rewrite help: copy-and-paste templates for quick fixes

If you find 'fastly' in a sentence, replace it with one of these depending on tone. Sometimes moving the adverb or rephrasing improves flow.

Work: "She submitted the report fastly to meet the deadline." → "She submitted the report quickly to meet the deadline."
Work (email): "Please review the attached fastly." → "Please review the attached document as soon as possible."
School: "The experiment ended fastly." → "The experiment ended quickly."
School: "He finished the homework fastly." → "He finished the homework quickly and uploaded it."
Casual: "I got there fastly." → "I got there fast."
Casual: "We completed it fastly." → "We completed it quickly." (or "We did it fast" for chat)
Press release: "The product shipped fastly to customers." → "The product shipped quickly to customers."
SMS / chat: "Fix was deployed fastly." → "Fix deployed - done fast."

Memory trick & editor habits to stop using 'fastly'

Mnemonic: think "ly → quickly." If the adverb of speed doesn't look like 'quickly' or another familiar '-ly' word, pause and check it.

Editor habits:

Search your draft for 'fastly' (and 'fast-ly') and replace with 'quickly' or 'fast' depending on tone.
Ask: "Is this formal?" If yes → use 'quickly.' If no → 'fast' is fine.
Run a final pass for invented -ly forms before sending or submitting.

Similar mistakes to watch for

Writers sometimes create nonstandard -ly forms or mix adjective/adverb forms. Catch these common errors instead of inventing new words.

Wrong: "He moved quick." - Better: "He moved quickly." (or "He moved fast" informally)
Wrong: "She answered swiftfully." - Better: "She answered swiftly."
Wrong: "goodly" (meant as 'well') - Better: "well"
Watch pairings like hard/hardly - they mean different things: "work hard" vs "hardly worked" (almost not).

Compare hard / hardly: Wrong: "He hardly worked on it" (if you mean he worked a lot).
Right: "He worked hard on it."

FAQ

Is 'fastly' a word?

You may see 'fastly' in historical texts, but it's archaic or nonstandard today. Use 'quickly' or 'fast' depending on tone.

Can I say "He finished the race fast"?

Yes. 'Fast' works as an adverb in informal speech and casual writing. For formal contexts, choose "He finished the race quickly."

When should I use 'rapidly' instead of 'quickly'?

Use 'rapidly' for a more technical or formal tone (science, technical reports). 'Quickly' is the safest neutral choice for general writing.

Will grammar checkers flag 'fast' as wrong?

Most tools accept 'fast' as a valid adverb. A few conservative checkers may prefer 'quickly' in very formal constructions; use 'quickly' if you want to be cautious.

How do I correct a sentence that currently uses 'fastly'?

Replace 'fastly' with 'quickly' for formal tone or 'fast' for informal tone. If needed, rephrase: "She finished quickly" or "She completed the task in record time."

Want a quick check?

If you often invent adverbs or worry about tone, try a grammar tool that highlights nonstandard forms (including 'fastly') and suggests context-appropriate alternatives. Paste your sentence and pick the rewrite that matches your audience.