diff --git a/relog-web/src/DictInputRow.js b/relog-web/src/DictInputRow.js
index 5ce6973..00f84a0 100644
--- a/relog-web/src/DictInputRow.js
+++ b/relog-web/src/DictInputRow.js
@@ -1,11 +1,11 @@
-import { useState } from 'react';
 import form_styles from './Form.module.css';
 import Button from './Button';
+import { validate } from './Form';
 
 const DictInputRow = (props) => {
     const dict = { ...props.value };
     if (!props.disableKeys) {
-        dict[""] = "";
+        dict[""] = "0";
     }
 
     let unit = "";
@@ -36,6 +36,15 @@ const DictInputRow = (props) => {
         if (index > 0) {
             label = "";
         }
+
+        let isValid = true;
+        if (props.validate !== undefined) {
+            isValid = validate(props.validate, dict[key]);
+        }
+
+        let className = "";
+        if (!isValid) className = form_styles.invalid;
+
         form.push(
             <div className={form_styles.FormRow} key={index}>
                 <label>{label}</label>
@@ -52,6 +61,7 @@ const DictInputRow = (props) => {
                     data-index={index}
                     value={dict[key]}
                     placeholder={props.valuePlaceholder}
+                    className={className}
                     onChange={e => onChangeValue(key, e.target.value)}
                 />
                 {tooltip}
diff --git a/relog-web/src/FileInputRow.js b/relog-web/src/FileInputRow.js
index 71239a9..a2b0099 100644
--- a/relog-web/src/FileInputRow.js
+++ b/relog-web/src/FileInputRow.js
@@ -2,7 +2,6 @@ import form_styles from './Form.module.css';
 import Button from './Button';
 
 const FileInputRow = (props) => {
-
     let tooltip = "";
     if (props.tooltip != undefined) {
         tooltip = <Button label="?" kind="inline" tooltip={props.tooltip} />;
@@ -10,7 +9,7 @@ const FileInputRow = (props) => {
 
     return <div className={form_styles.FormRow}>
         <label>{props.label}</label>
-        <input type="text" disabled="disabled" />
+        <input type="text" value={props.value} disabled="disabled" />
         <Button label="Upload" kind="inline" />
         <Button label="Clear" kind="inline" />
         <Button label="Template" kind="inline" />
diff --git a/relog-web/src/Form.js b/relog-web/src/Form.js
index e2c4607..4776a05 100644
--- a/relog-web/src/Form.js
+++ b/relog-web/src/Form.js
@@ -1,3 +1,17 @@
+const VALIDATION_REGEX = {
+    int: new RegExp('^[0-9]+$'),
+    intList: new RegExp('^\[[0-9]+(,[0-9]+)*\]$'),
+    float: new RegExp('^[0-9]*\\.?[0-9]*$'),
+};
+
+export const validate = (kind, value) => {
+    if (value.length == 0) return false;
+    if (!VALIDATION_REGEX[kind].test(value)) {
+        return false;
+    }
+    return true;
+};
+
 const Form = (props) => {
     return <>{props.children}</>;
 };
diff --git a/relog-web/src/Form.module.css b/relog-web/src/Form.module.css
index 4885c4e..8a508d0 100644
--- a/relog-web/src/Form.module.css
+++ b/relog-web/src/Form.module.css
@@ -20,4 +20,9 @@
 
 .FormRow_unit {
     color: rgba(0, 0, 0, 0.4);
+}
+
+.invalid {
+    border: 2px solid #faa !important;
+    background-color: rgba(255, 0, 0, 0.05);
 }
\ No newline at end of file
diff --git a/relog-web/src/InputPage.js b/relog-web/src/InputPage.js
index 9edd5d9..8c93220 100644
--- a/relog-web/src/InputPage.js
+++ b/relog-web/src/InputPage.js
@@ -12,7 +12,7 @@ const defaultData = {
     parameters: {
         "time horizon (years)": "1",
         "building period (years)": "[1]",
-        "annual inflation rate (%)": "0.0",
+        "annual inflation rate (%)": "0",
     },
     products: {
     },
@@ -21,15 +21,13 @@ const defaultData = {
 };
 
 const defaultProduct = {
-    "acquisition cost ($/tonne)": "0.00",
-    "disposal cost ($/tonne)": "0.00",
+    "initial amounts": {},
+    "acquisition cost ($/tonne)": "0",
+    "disposal cost ($/tonne)": "0",
     "disposal limit (tonne)": "0",
-    "transportation cost ($/km/tonne)": "0.00",
+    "transportation cost ($/km/tonne)": "0",
     "transportation energy (J/km/tonne)": "0",
-    "transportation emissions (J/km/tonne)": {
-        "CO2": 0,
-        "NH2": 0,
-    }
+    "transportation emissions (J/km/tonne)": {}
 };
 
 const randomPosition = () => {
diff --git a/relog-web/src/ParametersBlock.js b/relog-web/src/ParametersBlock.js
index 57fb950..1a7fc3f 100644
--- a/relog-web/src/ParametersBlock.js
+++ b/relog-web/src/ParametersBlock.js
@@ -19,6 +19,7 @@ const ParametersBlock = (props) => {
                         tooltip="Number of years in the simulation."
                         value={props.value["time horizon (years)"]}
                         onChange={v => onChangeField("time horizon (years)", v)}
+                        validate="int"
                     />
                     <TextInputRow
                         label="Building period"
@@ -26,6 +27,7 @@ const ParametersBlock = (props) => {
                         tooltip="List of years in which we are allowed to open new plants. For example, if this parameter is set to [1,2,3], we can only open plants during the first three years. By default, this equals [1]; that is, plants can only be opened during the first year."
                         value={props.value["building period (years)"]}
                         onChange={v => onChangeField("building period (years)", v)}
+                        validate="intList"
                     />
                     <TextInputRow
                         label="Annual inflation rate"
@@ -33,6 +35,7 @@ const ParametersBlock = (props) => {
                         tooltip="Rate of inflation applied to all costs."
                         value={props.value["annual inflation rate (%)"]}
                         onChange={v => onChangeField("annual inflation rate (%)", v)}
+                        validate="float"
                     />
                 </Form>
             </Card>
diff --git a/relog-web/src/ProductBlock.js b/relog-web/src/ProductBlock.js
index fb7dcac..f4379c0 100644
--- a/relog-web/src/ProductBlock.js
+++ b/relog-web/src/ProductBlock.js
@@ -13,6 +13,8 @@ const ProductBlock = (props) => {
         props.onChange(newProduct);
     };
 
+    const nCenters = Object.keys(props.value["initial amounts"]).length;
+
     return (
         <>
             <Section title={props.name} />
@@ -20,6 +22,7 @@ const ProductBlock = (props) => {
                 <Form>
                     <h1>General information</h1>
                     <FileInputRow
+                        value={`${nCenters} collection centers`}
                         label="Initial amounts"
                         tooltip="A dictionary mapping the name of each location to its description (see below). If this product is not initially available, this key may be omitted."
                     />
@@ -29,6 +32,7 @@ const ProductBlock = (props) => {
                         tooltip="The cost to acquire one tonne of this product from collection centers. Does not apply to plant outputs."
                         value={props.value["acquisition cost ($/tonne)"]}
                         onChange={v => onChange("acquisition cost ($/tonne)", v)}
+                        validate="float"
                     />
 
                     <h1>Disposal</h1>
@@ -38,6 +42,7 @@ const ProductBlock = (props) => {
                         tooltip="The cost to dispose of one tonne of this product at a collection center, without further processing. Does not apply to plant outputs."
                         value={props.value["disposal cost ($/tonne)"]}
                         onChange={v => onChange("disposal cost ($/tonne)", v)}
+                        validate="float"
                     />
                     <TextInputRow
                         label="Disposal limit"
@@ -45,6 +50,7 @@ const ProductBlock = (props) => {
                         tooltip="The maximum amount of this product that can be disposed of across all collection centers, without further processing."
                         value={props.value["disposal limit (tonne)"]}
                         onChange={v => onChange("disposal limit (tonne)", v)}
+                        validate="float"
                     />
 
                     <h1>Transportation</h1>
@@ -54,6 +60,7 @@ const ProductBlock = (props) => {
                         tooltip="The cost to transport this product."
                         value={props.value["transportation cost ($/km/tonne)"]}
                         onChange={v => onChange("transportation cost ($/km/tonne)", v)}
+                        validate="float"
                     />
                     <TextInputRow
                         label="Transportation energy"
@@ -61,15 +68,16 @@ const ProductBlock = (props) => {
                         tooltip="The energy required to transport this product."
                         value={props.value["transportation energy (J/km/tonne)"]}
                         onChange={v => onChange("transportation energy (J/km/tonne)", v)}
+                        validate="float"
                     />
                     <DictInputRow
                         label="Transportation emissions"
                         unit="J/km/tonne"
                         tooltip="A dictionary mapping the name of each greenhouse gas, produced to transport one tonne of this product along one kilometer, to the amount of gas produced (in tonnes)."
                         keyPlaceholder="Emission name"
-                        valuePlaceholder="0"
                         value={props.value["transportation emissions (J/km/tonne)"]}
                         onChange={v => onChange("transportation emissions (J/km/tonne)", v)}
+                        validate="float"
                     />
                 </Form>
             </Card>
diff --git a/relog-web/src/TextInputRow.js b/relog-web/src/TextInputRow.js
index 193e31a..13daf94 100644
--- a/relog-web/src/TextInputRow.js
+++ b/relog-web/src/TextInputRow.js
@@ -1,5 +1,6 @@
 import form_styles from './Form.module.css';
 import Button from './Button';
+import { validate } from './Form';
 
 const TextInputRow = (props) => {
     let unit = "";
@@ -12,6 +13,14 @@ const TextInputRow = (props) => {
         tooltip = <Button label="?" kind="inline" tooltip={props.tooltip} />;
     }
 
+    let isValid = true;
+    if (props.validate !== undefined) {
+        isValid = validate(props.validate, props.value);
+    }
+
+    let className = "";
+    if (!isValid) className = form_styles.invalid;
+
     return <div className={form_styles.FormRow}>
         <label>
             {props.label} {unit}
@@ -21,6 +30,7 @@ const TextInputRow = (props) => {
             placeholder={props.default}
             disabled={props.disabled}
             value={props.value}
+            className={className}
             onChange={e => props.onChange(e.target.value)}
         />
         {tooltip}