The best AI summarizer is usually a chatbot you already have: you put a document into Claude, ChatGPT or Gemini and say who the summary is for. Summarising is one of the AI use cases you can rely on every day, provided you check the result against the source.
The choice of tool matters less than the instruction. The length, the reader and the focus question decide whether you get a usable overview or a slick list of what was on the first few pages.
An AI summary sounds convincing, even when a figure or an exception is wrong. Checking figures, names and conclusions is therefore a fixed step, as is the question of which documents you put into an AI tool.
Scanned pages, tables and very long documents call for an adapted approach, because information drops out there without you noticing.
How do you summarise text with AI?
To summarise text with AI, work through four steps: prepare the source, give the instruction, read the result and check it against the source. Each step catches a different kind of mistake.
First put the complete document into the chat, as an upload or as pasted text. A summary of an extract misses the context of the rest, and the model usually does not point out on its own that something is missing.
Then state the purpose, the reader and the format you want in one message. A bare instruction such as “summarise” produces generic text that rarely fits what you want to do with it. Finally, read the result alongside the original.
Which AI summarizer should you use?
For an AI summarizer, use an AI chatbot that accepts files, such as Anthropic’s Claude, OpenAI’s ChatGPT or Google’s Gemini. According to Anthropic, Claude reads PDF, DOCX, CSV and TXT among other formats, with files of up to 500 MB and a maximum of 20 files per chat. In a project, the limit is 30 MB per file.
For analysing and summarising longer documents, such as annual reports and white papers, I use Claude myself. In my work, Claude loses less context than ChatGPT on long documents. I use Gemini within Google Workspace for summarising emails and spreadsheets.
Copilot in Word is an alternative if you work in Microsoft 365. According to Microsoft, Copilot in Word is included in the paid Personal, Family, Premium and new Pro plans, with AI credits, and not in the free Copilot app.
How do you control the length and focus of an AI summary?
You control the length and focus of an AI summary with three details in your instruction: the maximum number of words, the reader and the question the summary answers. A director making a decision looks for different information from a colleague taking over a case file.
An instruction that combines all three looks like this:
Summarise the attached advisory report in no more than 150 words for the board. Focus on the three recommendations and on the risk the report mentions if nothing is done. Put decisions and open questions in two separate lists.
If you leave out length, reader and focus question, you skip the building blocks of prompting. Without those details, a language model falls back on an average summary that would fit any document.
How do you check an AI summary?
You check an AI summary by tracing every specific statement back to the source: figures, names, dates and conclusions. Start with the points a decision rests on, because that is where a mistake costs the most.
During the period when I used ChatGPT intensively, I came across summaries that sounded plausible but differed in substance from the document. Such a deviation is a form of AI hallucination: the model fills in what sounds likely instead of what is actually there.
A practical check is the source question: have the model name the page or paragraph each point is based on, and read that passage yourself. Remove any point without an identifiable passage from the summary. From my years at major banks, I bring the four-eyes principle into AI work: nothing goes out without a second check, and that includes a summary.
Which documents can you summarise with AI?
Documents suitable for summarising with AI are those without confidential information or personal data, in a tool your organisation has approved. Contracts, client files and HR documents do not belong in a personal account on a free chatbot.
Your account type determines what happens to the text. In ChatGPT, switch off “Improve the model for everyone” in the data controls to prevent training on new conversations. OpenAI does not train on content from ChatGPT Business and Enterprise by default.
Anthropic only uses chats from Claude Free, Pro, Max and Ultra for training if the user opts in. Processing personal data in an AI tool without a legal basis and agreements with the processor breaches the GDPR. For that you need at least a business account with a data processing agreement.
What does AI summarise badly?
AI summarises three kinds of documents badly: documents with text in images, documents full of tables and documents longer than the model’s context window. In all three cases, information drops out without the summary showing it.
According to OpenAI, ChatGPT only extracts the digital text from an uploaded PDF and leaves out images, except in ChatGPT Enterprise. A scanned contract or a table embedded as an image in a PDF then never makes it into the summary.
For tables, ask for the figures with their row and column labels, so you can quickly find each amount again. Split documents that are too long into chapters and summarise each part separately. According to Anthropic, Claude tells you when a prompt exceeds the available context window.
Can you summarise a PDF with AI?
Yes, you can summarise a PDF with AI in Claude, ChatGPT and Gemini by uploading the file and asking for a summary with a length and reader. According to OpenAI, ChatGPT accepts documents of up to 512 MB and 2 million tokens per file. Check beforehand whether the PDF contains searchable text.
Can you summarise a meeting with AI?
Yes, you can summarise a meeting with AI using a transcript of the recording, which you then have the model turn into decisions and action points. Taking meeting notes with AI brings extra requirements, such as letting participants know in advance that you are recording.
Frequently asked questions about using an AI summarizer
You can also use AI to summarise sources that are not files, and in a different language from the original.
Can you summarise a YouTube video with AI?
Yes, you can summarise a YouTube video with AI in the Gemini app for Android, which uses public information from YouTube to answer questions about a video. According to Google’s help centre, you need to be signed in and have Keep Activity switched on. The feature does not work in Live conversations. Rewatch the passages a decision rests on yourself, just as you check a summary against the source document.
Can you summarise a web page with AI from a link?
Yes, you can summarise a web page with AI from a link in Claude if you have switched on web search. According to Anthropic, Claude then retrieves the content of a specific URL you paste into the chat. On a free account this counts towards your usage limit, and according to Anthropic a long page uses a good part of it. On Team and Enterprise, an administrator first has to switch on web search for the organisation.
Can you summarise a text in a different language from the original?
Yes, you can have an English text summarised in another language, such as Dutch or German, by naming the language you want in your instruction. Anthropic advises stating the input language and the output language explicitly, because that improves reliability. Watch the translation of specialist terms, because a legal or tax concept does not always have an equivalent in the target language. So leave doubtful terms in the source language, in brackets.
Where can you learn to summarise with AI without copying its mistakes?
LearnLLM’s Claude Course teaches you to summarise with AI without copying its mistakes. You analyse reports, contracts and policy documents, track down hallucinations and keep a verification log, with a practical assignment on your own work in each module.
