Free AI Letter Writer: Get AI Help Writing a Letter

To get AI help writing a letter, give a free AI chat tool (ChatGPT, Claude or Gemini) the letter type, the recipient, the facts it must include and the tone you want in one prompt, then edit the draft before you send it. 5 of the 6 AI letter writers compared below are free to start. For a cover letter tied to a job posting, ResuFit’s cover letter generator reads the posting and your resume and writes the letter for that job.

TL;DR

• The method: one prompt with 4 parts (letter type and recipient, facts, tone and length, format), then a fact check. A copy-ready prompt is below.
• Free to start: 5 of 6 tools here (ChatGPT, Claude, Gemini, Grammarly, ResuFit). Jasper has a 7-day trial, then paid plans.
• General letters: use a chat assistant. Cover letters for a specific job: ResuFit writes them in 5 languages (English, German, French, Spanish, Portuguese).
• Always verify: AI invents plausible details. Check every name, date and number.

What you’ll take away:

• A 4-step method that works in any AI chat tool
• A prompt template you can paste and fill in
• The free tier and price of 6 AI letter writers (checked September 2026)
• Which tool fits which kind of letter
• The mistakes that make AI letters sound generic

How do I get AI to help me write a letter?

Give the AI everything a human assistant would need, in one message. Most weak AI letters come from weak prompts (“write a letter to my landlord”). The AI then fills the gaps with generic phrases and invented details.

1. Say what the letter is and who reads it. “A formal complaint letter to the customer service department of my internet provider.”
2. List the facts it must use. Names, dates, account or order numbers, amounts, what happened, what you want. The AI cannot know these, so it will make them up if you leave them out.
3. Set the tone and length. “Polite but firm, under 200 words.” Tone is the part AI handles best once you name it.
4. Name the format convention. A US business letter, a UK formal letter and a German DIN 5008 letter are laid out differently. Our formal letter format guide covers the layouts, and the salutations guide covers how to open it.

Then read the draft line by line. Correct any fact it got wrong, delete sentences you would never say, and ask for a second version if the tone is off (“shorter and warmer”, “remove the second paragraph”).

A prompt template you can copy

Write a [letter type] from me, [your name], to [recipient name and role].
Purpose: [what you want the reader to do or know].
Facts to include: [dates, numbers, names, what happened].
Tone: [formal / friendly / firm], length: under [N] words.
Format: [US business letter / UK formal letter / email], with a subject line.
Do not invent any facts that are not listed above.

The last line matters. It tells the model to leave a gap instead of filling it with a plausible guess.

Which AI letter writer should I use?

Match the tool to the letter. General chat assistants handle any letter type. Specialized tools are better at one job.

Tool	Best for	Free to start	Paid plans (checked September 2026)	Job-posting workflow
ChatGPT	Any letter type	Yes	Go $8/month, Plus $20/month	Paste it in yourself
Claude	Tone-sensitive letters	Yes	Pro $20/month, or $17/month billed annually	Paste it in yourself
Google Gemini	Gmail and Google Docs users	Yes	Google AI Pro $19.99/month	Paste it in yourself
Grammarly	Polishing your own draft	Yes (100 AI prompts/month)	Pro $12/month billed annually	No
ResuFit	Cover letters for a specific job	Yes (generate and preview)	Pro unlocks the full download	Built in
Jasper	Business and marketing correspondence	7-day trial only	Pro $69/month, or $59/month billed annually	No

Prices are US list prices from each vendor’s pricing page (OpenAI, Anthropic, Google, Grammarly, Jasper) and change often. Check the vendor’s page before you pay.

The 6 AI letter writers compared

1. ChatGPT: best for any type of letter

OpenAI’s ChatGPT handles complaints, requests, reference letters, thank-you notes and resignation letters equally well when the prompt is specific. OpenAI states on its pricing page that the free version is available to everyone; the paid Go and Plus plans raise message limits and model access.

• Strengths: handles any letter type; large community of shared prompts; the free plan is enough for occasional letters
• Weaknesses: output quality depends on your prompt; no built-in job-posting workflow for cover letters (you paste the posting and write the prompt yourself)
• Price: free; Go $8/month; Plus $20/month

2. Claude: best for tone and nuance

Anthropic’s Claude is a good pick when tone carries the letter: a delicate request, a condolence note, a negotiation. It follows detailed instructions about register and length closely.

• Strengths: precise tone control; handles long instructions and pasted context
• Weaknesses: no letter-specific features; the free plan has usage limits
• Price: free; Pro $20/month, or $17/month billed annually (Anthropic pricing page)

3. Google Gemini: best if you live in Gmail and Docs

Gemini is free with a Google account, and the paid Google AI plans bring it into Gmail and Google Docs, where you can draft a letter in place.

• Strengths: free with a Google account; Workspace integration on paid plans; can read a screenshot of a document you need to answer
• Weaknesses: drafts can read formulaic without a detailed prompt
• Price: free; Google AI Pro $19.99/month in the US

4. Grammarly: best for polishing a letter you wrote

Grammarly works on your own draft. It fixes grammar, flags tone and rewrites sentences, and its free plan includes 100 AI prompts a month for generating text (Grammarly plans page).

• Strengths: works inside Gmail, Word and the browser; strong tone and clarity suggestions
• Weaknesses: full-sentence rewrites need Pro; weaker at writing a letter from nothing
• Price: free; Pro $12/month billed annually

For cover letters specifically, see the best AI software for editing cover letters.

5. ResuFit: best for cover letters tied to a job posting

ResuFit does one kind of letter. ResuFit’s cover letter generator reads the job posting you paste in, matches it against your resume, and writes a cover letter that uses the posting’s own requirements and wording, in 5 languages (English, German, French, Spanish, Portuguese). There is no prompt to write.

ChatGPT gives you a blank box. ResuFit writes the letter for the specific job.

• Strengths: reads the posting and your resume together; no prompt engineering; same workflow in 5 languages
• Weaknesses: cover letters and resumes only, not general letters
• Price: generating and previewing are free on a free account; the full cover letter download comes with Pro

Try it: generate a job-tailored cover letter and preview it free.

6. Jasper: best for business correspondence at scale

Jasper is a marketing platform. Brand-voice settings keep proposals, outreach letters and client communication consistent across a team.

• Strengths: brand voice and team features; built for high volume
• Weaknesses: no free plan (7-day trial of Pro); too much tool for a personal letter
• Price: Pro $69/month, or $59/month billed annually (Jasper pricing page)

Which letters is AI good at, and where should you be careful?

AI is strong at structure and tone, weak at facts. It will produce a well-formed letter for almost any purpose in seconds. It will also confidently fill any gap in your prompt with something plausible and wrong.

Letter type	Good tool	What to check yourself
Complaint or request	ChatGPT, Claude, Gemini	Order numbers, dates, the exact remedy you want
Reference or recommendation letter	ChatGPT, Claude	Every achievement it describes must be true and yours to vouch for
Resignation letter	ChatGPT, Claude	Notice period and last day (resignation letter guide)
Cover letter for a job	ResuFit	Your real results and dates; the posting’s company name
Business proposal letter	Jasper, ChatGPT	Prices, terms, legal wording

Tips for better AI letters

1. Paste the context. The email you are replying to or the job posting gives the AI far more to work with than a summary.
2. Ask for two versions. One formal, one warmer. Pick the better parts of each.
3. Keep your own details. A specific result or a name only you know is what separates your letter from every other AI draft.
4. Read it aloud. If a sentence sounds like a press release, rewrite it.
5. Check the format for the country. Salutations, date formats and closings differ between the US, UK, Germany, France, Spain and Brazil.

Write your cover letter for the job, free to preview

For any other letter, the prompt above and a free chat assistant are all you need. For a cover letter, ResuFit’s cover letter generator reads the job posting and writes the letter in 5 languages; generating and previewing are free, and the full download comes with Pro. A template gives you the layout. ResuFit writes the letter for the specific job. For more prompt ideas, see our AI prompts for cover letters and the guide to AI cover letter generators.