Introduction
Prompt engineering — the craft of designing inputs for AI language models — has a huge impact on the quality and consistency of the model’s output. Traditionally, prompts are written in plain natural language. However, a new approach called JSON prompting has been gaining traction among developers and AI enthusiasts . Instead of writing a request as free-form text, the idea is to structure the prompt as a JSON object with explicit fields. Proponents claim this technique yields more precise and reliable responses, especially for technical or structured tasks, while skeptics caution that it’s not a magic bullet for every situation . In this article, we’ll explore what regular (plain text) prompts are versus JSON-formatted prompts, how they differ, and how to use JSON prompts effectively — complete with examples, benefits, and limitations.
Photo by Ferenc Almasi on Unsplash
What is a Regular Prompt?
A regular prompt (or plain-text prompt) is simply a query or instruction given to an AI model in natural language. For example, a user might ask: “Summarize the customer feedback about shipping delays.” This kind of prompt relies on the model’s ability to interpret human language and figure out the task from context. Regular prompts are easy for humans to write, but they can sometimes be ambiguous or inconsistent. The model might misunderstand the request or produce outputs in an unpredictable format if the prompt isn’t specific enough. In other words, traditional prompting often feels like conversing with a “brilliant but inconsistent colleague” — you may get insightful answers, but their format and focus can vary . Developers using plain prompts sometimes struggle when they need the AI’s output to be strictly structured or directly parsed by software, since natural language responses can be verbose or inconsistent.
What is a JSON Prompt?
A JSON prompt is a prompt written as a JSON (JavaScript Object Notation) object, using keys and values to explicitly define the request. Instead of a free-form sentence, you “fill out” a structured template — much like entering parameters into a form . In a JSON prompt, each aspect of the task is a field. For instance, the same request above in JSON format could look like:
{ "task": "summarize", "topic": "customer feedback", "focus": "shipping delays"}
This format is machine-readable and unambiguous. Each key tells the model what kind of information or constraint you’re providing — e.g. “task” specifies the action, “topic” provides the subject matter, and “focus” might narrow down the aspect to emphasize . The model still ultimately sees a textual input (the JSON is text), but because the input is highly structured, the model can recognize the pattern and intent more easily. As one source puts it, “Not English. Not vibes. Just clear instructions.” — JSON prompts remove the guesswork by providing a rigid template of the user’s intent.
Example: Plain vs. JSON Prompt
To make the difference concrete, consider a simple task. A regular prompt might say:
“Can you write a tweet about dopamine detox?”
In contrast, a JSON-formatted prompt for the same request could be:
{ "task": "write a tweet", "topic": "dopamine detox", "style": "viral", "length": "under 280 characters"}
In the plain prompt, the model has to parse the sentence and may or may not infer the desired style or length. In the JSON prompt, we explicitly specified the style (“viral” tone) and length constraint. The JSON version is clear, modular, and explicitly structured, leaving less room for interpretation . You can already see how the JSON prompt acts like a mini-specification: the model is being instructed exactly what to do (write a tweet) and under what conditions (on the topic of dopamine detox, in a viral style, within 280 characters).
Why Use JSON Prompts? (Benefits)
Using JSON to structure a prompt offers several advantages for certain applications:
- Clarity and Reduced Ambiguity: JSON prompts significantly reduce ambiguity in instructions. By breaking down the request into discrete fields, you eliminate the vagueness that natural language can have . The model doesn’t have to “guess” your intent or the format of the answer — you’re telling it exactly what you want in a structured way. This often leads to more precise and on-point outputs.
- Consistency and Format Compliance: When you need the AI’s output in a specific format or to include certain elements, JSON prompting helps enforce that. The structured input serves like a contract for the output structure . In fact, many have reported that responses become far more consistent with the desired format. One informal report noted that using JSON formatting made the responses 80–90% more accurate and format-compliant (e.g. following instructions like “give me 5 bullet points” exactly) .
- Leverages Model Training Biases: Large language models have been trained on not just natural language, but also on lots of structured data: code, JSON, YAML, XML, configuration files, etc. This means they have seen patterns of keys, values, and structured syntax during training . When you present a prompt in JSON, the model likely recognizes it as a familiar pattern (similar to data or code) and treats it as a high-signal input. In other words, “Models like GPT learn from code, documentation, APIs, and organized data. JSON looks similar to what they were trained with, so they treat it as higher-signal” . The model doesn’t have to work as hard to parse your intent from a narrative sentence; instead, the structure directly maps to what it should do. This often reduces the chance of misunderstanding and can even reduce off-topic or “hallucinated” content, since the model is being funneled into a clear pattern .
- Easier Post-Processing and Integration: For developers, having the AI output follow a structure is gold. While the prompt format and output format are not the same thing, they’re related — if you prompt in JSON form, you’re implicitly guiding the model to output information in a structured manner too. Many find that JSON prompts make it easier to parse the results (sometimes you can even instruct the model to answer in JSON). In production systems, this is invaluable: “JSON prompting ensures that LLMs behave like dependable APIs” , meaning you can reliably extract fields from the response. This reduces the need for complex string parsing or regex on AI output. In fact, recognizing this trend, AI providers have started offering native support for structured outputs.
- Reusability and Modular Prompt Design: JSON prompts encourage you to separate content from instructions. This modular design means you can reuse prompt templates. For example, you might have a generic prompt like “Write a scientific summary using the provided context” and then feed different JSON blocks as the context (containing the study details, audience, tone, etc.) . By doing so, you create a flexible “prompting system” where the JSON defines the variables and the actual prompt can remain constant. This is extremely useful in enterprise settings — you can plug in new data (different product info, different user profiles, etc.) into a JSON template without rewriting the entire prompt each time .
How to Write a JSON Prompt
Using JSON in a prompt might feel unusual at first, but it essentially involves translating a request into a structured key-value specification. Here are some guidelines and best practices for writing effective JSON prompts :
- Identify the Key Parameters: Break down your task into elements like action, subject, style, format, constraints, etc. Each of these becomes a key in the JSON. Choose clear, descriptive key names. For example, use “task” for the action you want (e.g., “summarize”, “translate”), “topic” or “input” for the content to act on, “tone” for the style of writing, “length” for any length or format requirements, and so on. If the task involves an output format or specific fields, you can include a key like “output_format” or even a nested schema. The idea is to be explicit about everything. A regular prompt that says “Write a summary of this article for college students in 100 words” can be turned into JSON as:
{ "task": "summarize article", "audience": "college students", "length": "100 words", "tone": "curious"}
2. Use Nested Objects for Structure (if needed): JSON allows hierarchy. If your prompt has subcomponents or if the content can be grouped logically, use nested JSON objects. This can be useful for complex prompts. For example, suppose you want an AI to generate a Twitter thread with a specific structure: a hook, a body, and a call-to-action. You might nest those requirements under a "structure" key, like:
{ "task": "write a thread", "platform": "twitter", "structure": { "hook": "strong, short, curiosity-driven", "body": "3 core insights with examples", "cta": "ask a question to spark replies" }, "topic": "founder productivity systems"}
This nested JSON clearly organizes the prompt’s requirements . The model can see that under “structure”, it has specific instructions for different parts of the output. Nesting can help when there are categories of instructions or when you want to include example data separately from the main instruction.
3. Keep it Valid and Lean: Make sure your JSON syntax is correct (proper quotes, braces, etc.), because a malformed JSON might confuse the model (and won’t be parseable for you either!). Also, while adding structure, avoid unnecessary complexity. Use only as many fields as needed to convey your requirements. The goal is clarity, so don’t go overboard with deeply nested structures that might overwhelm the model. For instance, five to ten well-chosen fields might describe most tasks. If you have a very complex instruction set, consider whether it can be broken into multiple steps or prompts. Use comments or descriptions sparingly, if at all – remember the model sees everything, and extra fluff in the prompt can introduce ambiguity. Stick to the "key": "value" pairs of actual importance.
{ "task": "recommend books", "topic": "thinking clearly", "audience": "entrepreneurs", "output_format": "list of 5 with one-sentence summaries"}
This structured prompt explicitly asks for a list of 5 book recommendations on the topic of “thinking clearly” for an audience of entrepreneurs, and even specifies that each should have a one-sentence summary . By running both versions (the plain request vs the JSON), users have found that “the second one is sharper, easier to understand, and more on point.” The model, when given the JSON, is more likely to output exactly five bullet points, each with a concise description, because the prompt itself laid out that expectation clearly.
Tip: You can actually include the input text (if any) within the JSON as well. For instance, if the task is to improve some given writing, you can do: {“task”: “improve writing”, “input”: “<<<text>>>”, “criteria”: “make it concise and clear”}. This way, the model sees both the instruction and the text to act on in one structured blob. Many prompt engineers use delimiters or special markers even within JSON to clearly denote where the content is, but the key idea is to keep everything organized.
Limitations and When Not to Use JSON Prompts
While JSON-style prompting can be powerful, it’s not a silver bullet for all situations. There are important caveats and scenarios where a regular prompt may be more appropriate:
- Creative or Free-Form Tasks: If you ask the model for highly creative output (a poem, a story, an expressive essay) but wrap the prompt in a rigid JSON, you might stifle the model’s creativity. JSON syntax can put the model into a more literal, code-like frame of mind. In fact, the founder of PromptLayer noted an example: “Asking for ‘Write a love note and return it in JSON with key note’ produces worse results than simply ‘Write a love note.’” The model essentially “switched into technical mode” upon seeing the JSON structure, which hurt the creative quality of the output. This phenomenon is sometimes called a context switching penalty — the model’s style and thinking shift when you force a different format.
- Unnecessary Complexity and Token Overhead: JSON prompts, by nature, include extra characters (braces, quotes, keys) that a plain prompt wouldn’t have. This overhead can be non-trivial. Each character and token in the prompt counts toward the model’s context limit and can slightly increase processing time and cost. An OpenAI researcher pointed out that JSON can introduce a lot of “noise” for the model: whitespace and punctuation consume tokens, special characters have to be escaped, and the model has to keep track of all those brackets . In some cases, you might achieve the same clarity by just writing a well-formatted plain prompt or using Markdown lists, without the extra JSON syntax. Indeed, others have found that Markdown or other lightweight structure often performs just as well or better for certain tasks, since it’s less verbose and something models handle naturally too . The key is to avoid structuring the prompt in a more complicated way than the task actually requires.
- Pushing the Model into the Wrong Distribution: Large language models have different “modes” of behavior. When you wrap everything in JSON, you implicitly signal the model to treat this like data or code. That’s great for getting a structured response, but not great if you want a conversational or narrative style output. Over-structuring can constrain nuanced reasoning or stylistic richness. As one analysis put it, forcing JSON output can make the model pattern-match to technical documentation styles rather than natural human communication . So if the goal is a friendly chat or an open-ended brainstorm, a JSON prompt might make the responses too terse or formulaic.
- Not Always Statistically Better: While anecdotal reports and some studies praise JSON prompting, it’s not universally superior in all metrics. A research study in 2025 compared JSON prompting with other prompt styles (like YAML and a specialized CSV-based format) across tasks like parsing receipts and medical records. Interestingly, a highly compact Hybrid CSV/Prefix format slightly outperformed JSON in accuracy for those tasks (82% vs 74% accuracy on average), and was more efficient in terms of tokens and time . The differences weren’t always statistically significant, but the point is that JSON wasn’t the absolute winner in every case.
Conclusion & Summary
Regular prompts and JSON prompts are two different approaches to communicating with AI models, each with its own strengths. A regular prompt is written in natural language — it’s intuitive and flexible, but can be prone to ambiguity. A JSON prompt, on the other hand, turns your request into a structured specification — it’s explicit and precise, helping the AI to understand exactly what you want in a more deterministic way.
The rise of JSON prompting reflects a broader trend: as AI systems are increasingly used in production and automation, we require their outputs to be predictable and easy to integrate. JSON prompts bring a taste of software engineering discipline to AI querying, making the model’s behavior more like an API that returns structured data . This can dramatically cut down on errors, misinterpretations, and the time spent cleaning up AI output. In technical workflows (for instance, multi-step data processing or feeding AI outputs into databases), this reliability often “beats brilliance” — a slightly less eloquent but structured answer is usually more useful than a creative ramble that a program can’t parse .
However, JSON prompting is not about magically improving the model’s intelligence or creativity — it’s about improving communication and consistency. Critics rightly point out that it doesn’t make the core model better; it just makes the instructions clearer, which in turn can make results more consistently aligned with what you asked for . The real power comes when you as a developer or researcher harness the technique appropriately: know when to use it and when not to. As with any tool in AI, experimentation is key. Try formatting some of your prompts as JSON and compare the outputs to plain prompts. As one guide suggested, build small evaluations to see if JSON prompts help or hurt for your particular use case . Over time, you’ll develop an intuition for which parts of a task benefit from structure and which thrive with a bit of freedom.
In closing, JSON prompting is an exciting development in prompt engineering that bridges the gap between natural language flexibility and structured data precision. It offers a way to speak to AI models in a language they can follow with little ambiguity. Use it to command the AI when you need strict adherence and repeatability , but don’t be afraid to stick with regular prompts for those imaginative, open-ended conversations where a little unpredictability can be a good thing. By understanding the difference between regular and JSON prompts and wielding each in the right context, you can get the most out of AI models — whether you’re generating creative content or building robust AI-powered systems.
A message from our Founder
Hey, Sunil here. I wanted to take a moment to thank you for reading until the end and for being a part of this community.
Did you know that our team run these publications as a volunteer effort to over 200k supporters? We do not get paid by Medium!
If you want to show some love, please take a moment to follow me on LinkedIn, TikTok and Instagram.