> ## Documentation Index > Fetch the complete documentation index at: https://docs.platform.decart.ai/llms.txt > Use this file to discover all available pages before exploring further. # Prompting Guide > How to write effective prompts for Lucy 2.5, with templates and examples for every edit type. Lucy 2.5 edits video from a short written prompt and an optional reference image. Describe the visible change you want — what to add, replace, remove, restyle, transform, or preserve. Then say how the edit should interact with the subject and scene. Lucy 2.5 uses a structured prompt format. [Prompt enhancement](/models/realtime/streaming-best-practices#use-prompt-enhancement) (`enhance: true`) rewrites your instruction to fit the input video and any reference image. It is on by default; keep it on. **Prompt length.** Prompts have a maximum length. As a rough estimate, about 750 characters of English (around 120 words) fit. The exact limit depends on the wording, and other languages may allow fewer characters. If your prompt is too long, you get an error that tells you how many characters of it fit. This applies whether or not prompt enhancement is on. ## Basics Three inputs shape the result: * **Input video:** What Lucy can see and track. * **Reference image:** The visual material for an edit. It may not show every angle the video needs. * **Prompt:** The change you want. Describe the edit, not every visible detail — enhancement fills in the rest. ### Choosing an input video Lucy can only edit what it can clearly see and track. A good input video: * Keeps the subject fully visible and well lit. * Holds steady framing, and avoids fast motion, motion blur, and heavy occlusion. * Uses a clean, uncluttered background, especially for background edits. Lucy edits your live video in real time. Make sure the thing you want to edit is visible in the current frame — or name it explicitly in your prompt. ### Core prompting principles A strong prompt answers four questions, in four sentences or fewer: * **What should change?** Describe the intended result: a new appearance, object, character, or scene. * **Where is the change applied?** Anchor the edit to a visible location, such as a body part, garment detail, object surface, or background. * **How does it interact and move?** Say how the edit attaches to the subject and holds up as the subject moves. Name the physical behavior — attaches to, wraps around, trails with motion, reflects on, casts light on, or is occluded by — so the result tracks the subject instead of looking pasted on. * **What stays the same?** Name the details the edit should not affect, such as physical features, garment details, or objects. Together, those answers form one prompt:

```text Example: theme={null} Add blue smoke and white smoke to the person's shoulders. It follows their movement, billows outward, and passes behind their arms and body. Keep their face, clothing, and background unchanged. ```

This names the change (blue and white smoke), where it goes (on the shoulders), how it behaves (follows the person's movement, billows outward, and passes behind the arms and body), and what to preserve (face, clothing, and background). Make one focused edit per prompt. Combining several unrelated changes into one prompt makes each one less reliable — apply them one at a time. Cut filler adjectives like realistic, seamless, natural, cinematic, or high quality. Concrete visual details do more; use such words only when the look itself is the edit. Identify targets by visible details, not their position in the frame:

| ✅ Visible detail | ❌ Frame position | | ----------------------------------- | ------------------------ | | `"the red hat on the woman's head"` | `"the hat on the right"` |

If several similar objects appear, tell them apart by color, material, pattern, text, logo, or shape. Name each target with a concrete noun — the jacket, the left hand, the background — not a pronoun like it or this. ### Using reference images A reference image supplies the visual material for an edit — a garment, object, character, or art style. The prompt tells Lucy which part to use and how to apply it. Use a reference image when you need consistent results across different videos. Good reference images: * Show the intended item or style clearly and completely, with the full subject visible and centered. * Keep important details visible, such as shape, material, color, pattern, and fit. * Avoid cluttered backgrounds, occlusion, and extra people or objects. * Use a sharp, lightly compressed image, about 1280px on the longest side. * Pad unusual aspect ratios to the output orientation — 16:9 landscape or 9:16 portrait — instead of cropping or upscaling. Do not rely on an empty prompt. Even with a strong reference, specify the intended edit.

| ✅ Specific | ❌ Too general | | ------------------------------------------------------------------------------------- | --------------------------- | | `"Put the black leather jacket from the reference image on the person in the video."` | `"Put this on the person."` |

When using a reference image, your prompt should: * Name the item, character, or style to use. * Call out the visual details that matter, such as color, material, texture, shape, pattern, logo placement, or fit. * State where or how it should appear in the video. * Ignore reference details that are not part of the edit, such as the reference subject's pose, lighting, or background. ## Prompt templates and examples Each example starts on the unedited original clip, which shows the template for that edit type. Select a prompt beneath the video to see the edited result. Where a reference image was used, it appears next to the prompt. ### Character transformation

```text Template: theme={null} Replace the character in the video with . ``` ```text Prompt: theme={null} Replace the character in the video with a silver-armored space explorer with a reflective blue visor, white gloves, glowing shoulder lights, and a short navy cape. ``` ```text Prompt: theme={null} Replace the character in the video with a cheerful cartoon chef wearing a tall white hat, red neck scarf, double-breasted jacket, and round glasses. ```

```text Prompt: theme={null} Replace the character in the video with the Día de Muertos festival dancer from the reference image. She has tangerine and ivory face paint, an orange flower crown, a black dress with blue and orange floral embroidery, cream lace edging, a tiered skirt, and a fringed shawl. ```

Día de Muertos festival dancer reference image

**Tips** * Capture the character's defining traits, not just how it looks — its materials, textures, and how they move, like rigid armor, flowing fabric, or glowing energy. * Include distinctive details the reference may not show, such as wings, a tail, a shield, a backpack, or a cape. **Troubleshooting** * **If the person's face or identity changes:** This is the expected behavior – use Virtual Try-on (VTON) for costume changes that preserve identity.

| ✅ Do | ❌ Don't | | --------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------- | | `"Replace the shirt with a red silk blouse. Keep the person's identity, face, and hair unchanged."` | `"Change the person into someone wearing a red blouse."` — changes the person, not the shirt |

### Add objects

```text Template: theme={null} Add to . ``` ```text Prompt: theme={null} Add two blue, yellow, white, and green macaw parrots to each of the person's shoulders. ```

```text Prompt: theme={null} Add the sparkly blue helmet to the person's head. The helmet has wings, chrome flames, and a transparent yellow glass visor that shows the person's face inside. ```

```text Prompt: theme={null} Add a long sparkly blue cape attached to the person's shoulders. The cape has a stand collar, an opening for arms, silver trim, and a yellow inner fabric. ```

**Tips** * Describe the new object in detail — its parts, colors, and material properties. * When adding more than one, say how many and where each one goes.

| ✅ Do | ❌ Don't | | ----------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------- | | `"Add a silver crown floating above the person's head."` | `"Make it royal."` — too vague | | `"Glowing blue sparks emit from the person's fingertips, trail with their hand motion, and reflect on the person's fingers."` | `"A magical thing happens around the hands."` — too vague |

### Replace objects or features

```text Template: theme={null} Replace with . ```

```text Prompt: theme={null} Replace the person's sunglasses with the heart-shaped sunglasses, including the glossy hot-pink frame and mirrored rose-tint lenses. ```

```text Prompt: theme={null} Replace the plants in the background with tropical foliage. ``` ```text Prompt: theme={null} Replace the fence with a waterfall-style fountain along the edge of the deck. ```

**Tips** * To change many similar elements, name the category — like the plants in the background — instead of listing each one. * Describe what you want to see, not how the edit should be done. **Troubleshooting** * **If the original still shows through the replacement:** Describe the new object in full, including the parts that should change.

| ✅ Do | ❌ Don't | | ------------------------------------------------------------------------------------------------------------------------------------ | -------------------------------------------- | | `"Replace the person's sunglasses with heart-shaped sunglasses, including the glossy hot-pink frame and mirrored rose-tint lenses."` | `"Change the glasses."` — no visible details |

### Change attribute

```text Template: theme={null} Change