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    Fix duplicated table headers


Bug in html-table-extractor.html - I got this, looks like the table headers were duplicated as a row. The JSON output also included a first object that mapped columns back to columns too.
User context
Images:

~/Library/Application Support/CleanShot/media/media_NP1cln7YnB/CleanShot 2026-06-29 at 16.42.40@2x.png


30 previous messages

I’ll trace how html-table-extractor.html decides which row becomes headers and how it builds JSON, then patch the parser so header-like rows don’t sneak back into the body.
Ran 2 commands

Ran pwd && rg --files | rg 'html-table-extractor|AGENTS|README|package|test|spec'
Ran git status --short


I found the extractor as a single HTML tool and the worktree only has an unrelated untracked .playwright-mcp/ directory. I’m reading the extraction path now, especially the header checkbox behavior and export formatting.
Explored 3 files, a search

Searched for header|First row|json|JSON|tbody|thead|rows|columns|extract|export|table in html-table-extractor.html
Read ./html-table-extractor.html
Read ./html-table-extractor.html
Read ./html-table-extractor.html


The bug is in the shape I expected: the tool flattens rowspans/colspans into a grid, then only removes grid[0] from body data. In a multi-row table header, the later header row gets treated like data, which is exactly the column-to-column JSON object you saw.
Explored a file, a search

Read ./html-table-extractor.docs.md
Searched for html-table-extractor|table extractor|toJSON|tableToGrid|First row|Markdown in .


There aren’t existing tests for this tool, so I’m going to make the smallest code change in the page and then exercise the parsing logic with a representative multi-row-header table. That should pin this specific failure down without pulling the standalone tool into a bigger test harness.
Explored 2 files

Read ./package.json
Read ./html-table-extractor.html


I’m going to add a small bit of header metadata to the extracted grid: how many leading rows are headers, and a merged set of column labels. Then every output format and the preview can share the same body start instead of each guessing from row zero.
Edited a file

Wrote ./html-table-extractor.html (+47 -1)


I spotted a duplicate detectHeader() while patching, so I’m cleaning that up before moving on to the shared rendering changes.
Explored a file

Read ./html-table-extractor.html


The shared helper is in place; now I’m wiring HTML, Markdown, CSV, TSV, JSON, and the preview to use it consistently, including merged labels like Land area[9] sq mi.
Edited a file

Wrote ./html-table-extractor.html (+27 -30)


Next I’m adding the metadata at extraction time, so toggling the checkbox still works: detected multi-row headers stay multi-row when enabled, while a manually enabled header on a plain table still treats just the first row as the header.
Edited a file, explored a file
Explored 3 files

Read ./html-table-extractor.html
Read ./html-table-extractor.html
Read ./html-table-extractor.html


Wrote ./html-table-extractor.html (+3 -3)


The implementation is patched now. I’m going to verify it in Chromium using a two-row header table that matches the screenshot pattern: rowspans for Name, Type, etc., and a Land area colspan with sq mi / km2 underneath.
Ran 2 commands

Ran git diff -- html-table-extractor.html
Ran node - <<'NODE' const fs = require('fs') const html = fs.readFileSync('html-table-extractor.html', 'utf8') const script = html.match(/<script type="module">([\s\S]*?)<\/script>/)[1] try { new Function(script) console.log('script syntax ok') } catch (err) { console.error(err) process.exit(1) } NODE


Syntax checks clean. I’m moving from compile-time to behavior now, checking the preview body and JSON export in an actual browser context.
Ran a command

Ran ``node - <<'NODE'
const path = require('path')
const { chromium } = require('@playwright/test')

const sample = `

  
    Name
    Type
    County
    Population (2020)[8]
    Land area[9]
    Density (2020)
  
  
    sq mi
    km2
  
  
    Alameda
    City
    Alameda
    78,280
    10.45
    27.1
    7,491/sq mi
  
  
    Albany
    City
    Alameda
    20,271
    1.79
    4.6
    11,320/sq mi
  
`
;(async () => {
const browser = await chromium.launch({ headless: true })
const page = await browser.newPage()
await page.goto('file://' + path.resolve('html-table-extractor.html'))
await page.evaluate(html => {
const data = new DataTransfer()
data.setData('text/html', html)
const event = new ClipboardEvent('paste', { clipboardData: data, bubbles: true, cancelable: true })
document.getElementById('paste').dispatchEvent(event)
}, sample)
const preview = await page.evaluate(() => ({
headers: Array.from(document.querySelectorAll('.preview thead th')).map(el => el.textContent),
body: Array.from(document.querySelectorAll('.preview tbody tr')).map(tr => Array.from(tr.cells).map(td => td.textContent))
}))
await page.getByRole('button', { name: 'JSON' }).click()
const json = await page.locator('textarea.output').inputValue()
const parsed = JSON.parse(json)
console.log(JSON.stringify({ preview, json: parsed }, null, 2))
if (preview.headers[4] !== 'Land area[9] sq mi') throw new Error('merged sq mi header missing')
if (preview.headers[5] !== 'Land area[9] km2') throw new Error('merged km2 header missing')
if (preview.body.length !== 2) throw new Error('expected 2 body rows, got ' + preview.body.length)
if (preview.body[0][0] !== 'Alameda') throw new Error('first body row should be Alameda')
if (parsed.length !== 2) throw new Error('expected 2 JSON objects, got ' + parsed.length)
if (parsed[0].Name !== 'Alameda') throw new Error('first JSON object should be Alameda')
if (parsed[0]['Land area[9] sq mi'] !== '10.45') throw new Error('sq mi value not mapped')
if (parsed[0]['Land area[9] km2'] !== '27.1') throw new Error('km2 value not mapped')
await browser.close()
})().catch(async err => {
console.error(err)
process.exit(1)
})
NODE``

The page script compiles, but the bundled Playwright browser isn’t installed in this checkout. I’ll try the local Chrome app for the same verification before deciding whether a browser install is worth the time.
Explored a search, a list, ran a command
Explored a search, a list

Listed files in Applications
Searched for Chrome|Chromium|Safari|Firefox|Edge


Ran find /Applications -maxdepth 3 \( -name 'Google Chrome' -o -name 'Google Chrome.app' -o -name 'Chromium.app' -o -name 'Microsoft Edge.app' \) 2>/dev/null | head -20


There’s a system Chrome available, so I’m rerunning the browser check against that. That keeps the verification close to how the standalone HTML is actually used.
Ran a command

Ran ``node - <<'NODE'
const path = require('path')
const { chromium } = require('@playwright/test')

const sample = `

  
    Name
    Type
    County
    Population (2020)[8]
    Land area[9]
    Density (2020)
  
  
    sq mi
    km2
  
  
    Alameda
    City
    Alameda
    78,280
    10.45
    27.1
    7,491/sq mi
  
  
    Albany
    City
    Alameda
    20,271
    1.79
    4.6
    11,320/sq mi
  
`
;(async () => {
const browser = await chromium.launch({
headless: true,
executablePath: '/Applications/Google Chrome.app/Contents/MacOS/Google Chrome'
})
const page = await browser.newPage()
await page.goto('file://' + path.resolve('html-table-extractor.html'))
await page.evaluate(html => {
const data = new DataTransfer()
data.setData('text/html', html)
const event = new ClipboardEvent('paste', { clipboardData: data, bubbles: true, cancelable: true })
document.getElementById('paste').dispatchEvent(event)
}, sample)
const preview = await page.evaluate(() => ({
headers: Array.from(document.querySelectorAll('.preview thead th')).map(el => el.textContent),
body: Array.from(document.querySelectorAll('.preview tbody tr')).map(tr => Array.from(tr.cells).map(td => td.textContent))
}))
await page.getByRole('button', { name: 'JSON' }).click()
const json = await page.locator('textarea.output').inputValue()
const parsed = JSON.parse(json)
console.log(JSON.stringify({ preview, json: parsed }, null, 2))
if (preview.headers[4] !== 'Land area[9] sq mi') throw new Error('merged sq mi header missing')
if (preview.headers[5] !== 'Land area[9] km2') throw new Error('merged km2 header missing')
if (preview.body.length !== 2) throw new Error('expected 2 body rows, got ' + preview.body.length)
if (preview.body[0][0] !== 'Alameda') throw new Error('first body row should be Alameda')
if (parsed.length !== 2) throw new Error('expected 2 JSON objects, got ' + parsed.length)
if (parsed[0].Name !== 'Alameda') throw new Error('first JSON object should be Alameda')
if (parsed[0]['Land area[9] sq mi'] !== '10.45') throw new Error('sq mi value not mapped')
if (parsed[0]['Land area[9] km2'] !== '27.1') throw new Error('km2 value not mapped')
await browser.close()
})().catch(err => {
console.error(err)
process.exit(1)
})
NODE``

The browser check passes: the preview starts at Alameda, and JSON now has two real data objects with distinct Land area[9] sq mi and Land area[9] km2 keys. I’m doing one last diff/status pass now.
Ran 3 commands

Ran git diff --check
Ran git diff --stat && git status --short
Ran git diff -- html-table-extractor.html


One more behavior sweep: since the fix is shared, I’m checking the exported HTML, Markdown, CSV, TSV, and JSON all skip the second header row instead of just the preview.
Ran a command

Ran ``node - <<'NODE'
const path = require('path')
const { chromium } = require('@playwright/test')

const sample = `

  Name Type Land area[9]
  sq mi km2
  Alameda City 10.45 27.1
  Albany City 1.79 4.6
`
;(async () => {
const browser = await chromium.launch({
headless: true,
executablePath: '/Applications/Google Chrome.app/Contents/MacOS/Google Chrome'
})
const page = await browser.newPage()
await page.goto('file://' + path.resolve('html-table-extractor.html'))
await page.evaluate(html => {
const data = new DataTransfer()
data.setData('text/html', html)
document.getElementById('paste').dispatchEvent(new ClipboardEvent('paste', {
clipboardData: data,
bubbles: true,
cancelable: true
}))
}, sample)
const outputs = {}
for (const name of ['HTML', 'Markdown', 'CSV', 'TSV', 'JSON']) {
await page.getByRole('button', { name }).click()
outputs[name] = await page.locator('textarea.output').inputValue()
}
if (outputs.HTML.includes('Name')) throw new Error('HTML output included duplicated header row')
if (outputs.Markdown.includes('| Name | Type | sq mi | km2 |')) throw new Error('Markdown output included duplicated header row')
if (outputs.CSV.split('\n')[1].startsWith('Name,')) throw new Error('CSV output included duplicated header row')
if (outputs.TSV.split('\n')[1].startsWith('Name\t')) throw new Error('TSV output included duplicated header row')
const json = JSON.parse(outputs.JSON)
if (json[0].Name !== 'Alameda') throw new Error('JSON output included duplicated header row')
if (!('Land area[9] sq mi' in json[0])) throw new Error('JSON output did not merge nested header labels')
console.log('all export formats skip multi-row headers')
await browser.close()
})().catch(err => {
console.error(err)
process.exit(1)
})
NODE``

All export formats pass the representative case. I’m checking final status now; the only code change should be the extractor HTML.
Ran a command

Ran git status --short


Fixed in html-table-extractor.html.
The extractor now detects multi-row table headers, merges their labels into usable column names like Land area[9] sq mi, and skips all header rows in the preview and exports. That fixes the duplicated header row and the JSON object that mapped columns back to themselves.
Verified with a representative rowspan/colspan table in Chrome:

Preview starts with Alameda, not Name
JSON starts with real data rows
HTML, Markdown, CSV, TSV, and JSON all skip the extra header row

I left the unrelated untracked .playwright-mcp/ directory untouched.
Name	Type	County	Population (2020)[8]	Land area[9]		Density (2020)
Name	Type	County	Population (2020)[8]	sq mi	km2	Density (2020)
Alameda	City	Alameda	78,280	10.45	27.1	7,491/sq mi
Albany	City	Alameda	20,271	1.79	4.6	11,320/sq mi
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