diff --git a/bin/chat.js b/bin/chat.js
index 2789f8ee..f4be69c3 100644
--- a/bin/chat.js
+++ b/bin/chat.js
@@ -1,15 +1,14 @@
 import { tools } from './tools.js'
 
-const systemPrompt =
-  'You are a machine learning web application named "hyperparam". ' +
-  'You assist users with building high quality ML models by introspecting on their training set data. ' +
-  'The website and api are available at hyperparam.app. ' +
-  'Hyperparam uses LLMs to analyze their own training set. ' +
-  'It can generate the perplexity, entropy, and other metrics of the training set. ' +
-  'This allows users to find segments of their data set which are difficult to model. ' +
-  'This could be because the data is junk, or because the data requires deeper understanding. ' +
-  'This is essential for closing the loop on the ML lifecycle. ' +
-  'The quickest way to get started is to upload a dataset and start exploring.'
+const systemPrompt = 'You are a machine learning web application named "Hyperparam".'
+  + ' You assist users with building high quality ML models by introspecting on their training set data.'
+  + ' The website and api are available at hyperparam.app.'
+  + ' Hyperparam uses LLMs to analyze their own training set.'
+  + ' It can generate the perplexity, entropy, and other metrics of the training set.'
+  + ' This allows users to find segments of their data set which are difficult to model.'
+  + ' This could be because the data is junk, or because the data requires deeper understanding.'
+  + ' This is essential for closing the loop on the ML lifecycle.'
+  + ' The quickest way to get started is to upload a dataset and start exploring.'
 /** @type {Message} */
 const systemMessage = { role: 'system', content: systemPrompt }
 
@@ -27,7 +26,7 @@ const colors = {
  * @returns {Promise<Message>}
  */
 async function sendToServer(chatInput) {
-  const response = await fetch('http://localhost:3000/api/functions/openai/chat', {
+  const response = await fetch('https://hyperparam.app/api/functions/openai/chat', {
     method: 'POST',
     headers: { 'Content-Type': 'application/json' },
     body: JSON.stringify(chatInput),
@@ -38,8 +37,10 @@ async function sendToServer(chatInput) {
   }
 
   // Process the streaming response
+  /** @type {Message} */
   const streamResponse = { role: 'assistant', content: '' }
-  const reader = response.body.getReader()
+  const reader = response.body?.getReader()
+  if (!reader) throw new Error('No response body')
   const decoder = new TextDecoder()
   let buffer = ''
 
@@ -53,19 +54,19 @@ async function sendToServer(chatInput) {
     for (const line of lines) {
       if (!line.trim()) continue
       try {
-        const jsonChunk = JSON.parse(line)
-        const { content, error } = jsonChunk
-        if (content) {
-          streamResponse.content += content
-          write(content)
+        const chunk = JSON.parse(line)
+        const { type, error } = chunk
+        if (type === 'response.output_text.delta') {
+          streamResponse.content += chunk.delta
+          write(chunk.delta)
         } else if (error) {
           console.error(error)
           throw new Error(error)
-        } else if (jsonChunk.function) {
+        } else if (chunk.function) {
           streamResponse.tool_calls ??= []
-          streamResponse.tool_calls.push(jsonChunk)
-        } else if (!jsonChunk.key && jsonChunk.content !== '') {
-          console.log('Unknown chunk', jsonChunk)
+          streamResponse.tool_calls.push(chunk)
+        } else if (!chunk.key) {
+          console.log('Unknown chunk', chunk)
         }
       } catch (err) {
         console.error('Error parsing chunk', err)
@@ -85,6 +86,7 @@ async function sendToServer(chatInput) {
  */
 async function sendMessages(messages) {
   const chatInput = {
+    model: 'gpt-4o',
     messages,
     tools: tools.map(tool => tool.tool),
   }
@@ -92,12 +94,13 @@ async function sendMessages(messages) {
   messages.push(response)
   // handle tool results
   if (response.tool_calls) {
-    /** @type {{ toolCall: ToolCall, tool: ToolHandler, result: Promise<Message> }[]} */
+    /** @type {{ toolCall: ToolCall, tool: ToolHandler, result: Promise<string> }[]} */
     const toolResults = []
     for (const toolCall of response.tool_calls) {
       const tool = tools.find(tool => tool.tool.function.name === toolCall.function.name)
       if (tool) {
-        const result = tool.handleToolCall(toolCall)
+        const args = JSON.parse(toolCall.function?.arguments ?? '{}')
+        const result = tool.handleToolCall(args)
         toolResults.push({ toolCall, tool, result })
       } else {
         throw new Error(`Unknown tool: ${toolCall.function.name}`)
@@ -106,24 +109,27 @@ async function sendMessages(messages) {
     write('\n')
     for (const toolResult of toolResults) {
       const { toolCall, tool } = toolResult
-      const result = await toolResult.result
+      try {
+        const content = await toolResult.result
 
-      // Construct function call message
-      const args = JSON.parse(toolCall.function?.arguments ?? '{}')
-      const keys = Object.keys(args)
-      let func = toolCall.function.name
-      if (keys.length === 0) {
-        func += '()'
-      } else if (keys.length === 1) {
-        func += `(${args[keys[0]]})`
-      } else {
-        // transform to (arg1 = 111, arg2 = 222)
-        const pairs = keys.map(key => `${key} = ${args[key]}`)
-        func += `(${pairs.join(', ')})`
-      }
+        // Construct function call message
+        const args = JSON.parse(toolCall.function?.arguments ?? '{}')
+        const entries = Object.entries(args)
+        let func = toolCall.function.name
+        if (entries.length === 0) {
+          func += '()'
+        } else {
+          // transform to (arg1 = 111, arg2 = 222)
+          const pairs = entries.map(([key, value]) => `${key} = ${value}`)
+          func += `(${pairs.join(', ')})`
+        }
 
-      write(colors.tool, `${tool.emoji} ${func}`, colors.normal, '\n\n')
-      messages.push(result)
+        write(colors.tool, `${tool.emoji} ${func}`, colors.normal, '\n\n')
+        messages.push({ role: 'tool', content, tool_call_id: toolCall.id })
+      } catch (error) {
+        write(colors.error, `\nError calling tool ${toolCall.function.name}: ${error.message}\n\n`, colors.normal)
+        messages.push({ role: 'tool', content: `Error calling tool ${toolCall.function.name}: ${error.message}`, tool_call_id: toolCall.id })
+      }
     }
     // send messages with tool results
     await sendMessages(messages)
diff --git a/bin/serve.js b/bin/serve.js
index 94a69789..a5f3abaf 100644
--- a/bin/serve.js
+++ b/bin/serve.js
@@ -123,7 +123,7 @@ async function handleStatic(filePath, range) {
   if (!stats?.isFile()) {
     return { status: 404, content: 'not found' }
   }
-  const contentLength = stats.size
+  const fileSize = stats.size
 
   // detect content type
   const extname = path.extname(filePath)
@@ -133,8 +133,8 @@ async function handleStatic(filePath, range) {
   // ranged requests
   if (range) {
     const [unit, ranges] = range.split('=')
-    if (unit === 'bytes') {
-      const [start, end] = ranges.split('-').map(Number)
+    if (unit === 'bytes' && ranges) {
+      const [start = 0, end = fileSize] = ranges.split('-').map(Number)
 
       // convert fs.ReadStream to web stream
       const fsStream = createReadStream(filePath, { start, end })
@@ -151,7 +151,7 @@ async function handleStatic(filePath, range) {
   }
 
   const content = await fs.readFile(filePath)
-  return { status: 200, content, contentLength, contentType }
+  return { status: 200, content, contentLength: fileSize, contentType }
 }
 
 /**
diff --git a/bin/tools.js b/bin/tools.js
index 8dcd9067..3a89d258 100644
--- a/bin/tools.js
+++ b/bin/tools.js
@@ -1,8 +1,10 @@
 import fs from 'fs/promises'
 import { asyncBufferFromFile, parquetQuery, toJson } from 'hyparquet'
+import { compressors } from 'hyparquet-compressors'
 
+const fileLimit = 20 // limit to 20 files per page
 /**
- * @import { Message, ToolCall, ToolHandler } from './types.d.ts'
+ * @import { ToolHandler } from './types.d.ts'
  * @type {ToolHandler[]}
  */
 export const tools = [
@@ -12,29 +14,47 @@ export const tools = [
       type: 'function',
       function: {
         name: 'list_files',
-        description: 'List the files in the current directory.',
+        description: `List the files in a directory. Files are listed recursively up to ${fileLimit} per page.`,
         parameters: {
           type: 'object',
           properties: {
-            path: { type: 'string', description: 'The path to list files from (optional).' },
+            path: {
+              type: 'string',
+              description: 'The path to list files from. Optional, defaults to the current directory.',
+            },
+            filetype: {
+              type: 'string',
+              description: 'Optional file type to filter by, e.g. "parquet", "csv". If not provided, all files are listed.',
+            },
+            offset: {
+              type: 'number',
+              description: 'Skip offset number of files in the listing. Defaults to 0. Optional.',
+            },
           },
         },
       },
     },
     /**
-     * @param {ToolCall} toolCall
-     * @returns {Promise<Message>}
+     * @param {Record<string, unknown>} args
+     * @returns {Promise<string>}
      */
-    async handleToolCall(toolCall) {
-      let { path = '.' } = JSON.parse(toolCall.function.arguments || '{}')
+    async handleToolCall({ path = '.', filetype, offset = 0 }) {
+      if (typeof path !== 'string') {
+        throw new Error('Expected path to be a string')
+      }
       if (path.includes('..') || path.includes('~')) {
         throw new Error('Invalid path: ' + path)
       }
-      // append to current directory
-      path = process.cwd() + '/' + path
-      // list files in the current directory
-      const filenames = await fs.readdir(path)
-      return { role: 'tool', content: `Files:\n${filenames.join('\n')}`, tool_call_id: toolCall.id }
+      if (typeof filetype !== 'undefined' && typeof filetype !== 'string') {
+        throw new Error('Expected filetype to be a string or undefined')
+      }
+      const start = validateInteger('offset', offset, 0)
+      // list files in the directory
+      const filenames = (await fs.readdir(path))
+        .filter(key => !filetype || key.endsWith(`.${filetype}`)) // filter by file type if provided
+      const limited = filenames.slice(start, start + fileLimit)
+      const end = start + limited.length
+      return `Files ${start + 1}..${end} of ${filenames.length}:\n${limited.join('\n')}`
     },
   },
   {
@@ -42,36 +62,78 @@ export const tools = [
     tool: {
       type: 'function',
       function: {
-        name: 'read_parquet',
-        description: 'Read rows from a parquet file. Do not request more than 5 rows.',
+        name: 'parquet_get_rows',
+        description: 'Get up to 5 rows of data from a parquet file.',
         parameters: {
           type: 'object',
           properties: {
-            filename: { type: 'string', description: 'The name of the parquet file to read.' },
-            rowStart: { type: 'integer', description: 'The start row index.' },
-            rowEnd: { type: 'integer', description: 'The end row index.' },
-            orderBy: { type: 'string', description: 'The column name to sort by.' },
+            filename: {
+              type: 'string',
+              description: 'The name of the parquet file to read.',
+            },
+            offset: {
+              type: 'number',
+              description: 'The starting row index to fetch (0-indexed).',
+            },
+            limit: {
+              type: 'number',
+              description: 'The number of rows to fetch. Default 5. Maximum 5.',
+            },
+            orderBy: {
+              type: 'string',
+              description: 'The column name to sort by.',
+            },
           },
           required: ['filename'],
         },
       },
     },
     /**
-     * @param {ToolCall} toolCall
-     * @returns {Promise<Message>}
+     * @param {Record<string, unknown>} args
+     * @returns {Promise<string>}
      */
-    async handleToolCall(toolCall) {
-      const { filename, rowStart = 0, rowEnd = 5, orderBy } = JSON.parse(toolCall.function.arguments || '{}')
-      if (rowEnd - rowStart > 5) {
-        throw new Error('Do NOT request more than 5 rows.')
+    async handleToolCall({ filename, offset = 0, limit = 5, orderBy }) {
+      if (typeof filename !== 'string') {
+        throw new Error('Expected filename to be a string')
+      }
+      const rowStart = validateInteger('offset', offset, 0)
+      const rowEnd = rowStart + validateInteger('limit', limit, 1, 5)
+      if (typeof orderBy !== 'undefined' && typeof orderBy !== 'string') {
+        throw new Error('Expected orderBy to be a string')
       }
       const file = await asyncBufferFromFile(filename)
-      const rows = await parquetQuery({ file, rowStart, rowEnd, orderBy })
+      const rows = await parquetQuery({ file, rowStart, rowEnd, orderBy, compressors })
       let content = ''
       for (let i = rowStart; i < rowEnd; i++) {
-        content += `Row ${i}: ${JSON.stringify(toJson(rows[i]))}\n`
+        content += `Row ${i}: ${stringify(rows[i])}\n`
       }
-      return { role: 'tool', content, tool_call_id: toolCall.id }
+      return content
     },
   },
 ]
+
+/**
+ * Validates that a value is an integer within the specified range. Max is inclusive.
+ * @param {string} name - The name of the value being validated.
+ * @param {unknown} value - The value to validate.
+ * @param {number} min - The minimum allowed value (inclusive).
+ * @param {number} [max] - The maximum allowed value (inclusive).
+ * @returns {number}
+ */
+function validateInteger(name, value, min, max) {
+  if (typeof value !== 'number' || isNaN(value)) {
+    throw new Error(`Invalid number for ${name}: ${value}`)
+  }
+  if (!Number.isInteger(value)) {
+    throw new Error(`Invalid number for ${name}: ${value}. Must be an integer.`)
+  }
+  if (value < min || max !== undefined && value > max) {
+    throw new Error(`Invalid number for ${name}: ${value}. Must be between ${min} and ${max}.`)
+  }
+  return value
+}
+
+function stringify(obj, limit = 1000) {
+  const str = JSON.stringify(toJson(obj))
+  return str.length <= limit ? str : str.slice(0, limit) + '…'
+}
diff --git a/bin/types.d.ts b/bin/types.d.ts
index cff9a024..308dc526 100644
--- a/bin/types.d.ts
+++ b/bin/types.d.ts
@@ -20,7 +20,7 @@ export interface Message {
 export interface ToolHandler {
   emoji: string
   tool: Tool
-  handleToolCall(toolCall: ToolCall): Promise<Message>
+  handleToolCall(args: Record<string, unknown>): Promise<string>
 }
 interface ToolProperty {
   type: string
diff --git a/tsconfig.json b/tsconfig.json
index 3d90c573..8e8280ec 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,5 +1,7 @@
 {
   "compilerOptions": {
+    "allowJs": true,
+    "checkJs": true,
     "target": "es2022",
     "useDefineForClassFields": true,
     "lib": ["es2022", "DOM", "DOM.Iterable"],