CSS Design Calc
Estimate characters per line from column width and font size and rate it for readability (45-75 ideal, WCAG max 80).
OtherLiveeip155:8453Exactvia cdp
CssTypographyReadabilityAccessibility
Calls · 30d
1
This endpoint's own trailing-30-day call count, as published by the upstream catalog and snapshotted daily. 4 snapshots so far.
$24.31
Verified settled volume
1,175 settlements proven x402 by their on-chain EIP-3009 marker.
$0.020
Listed price
As published in the catalog. Always read the live 402 before paying.
1
Calls · 30d
Upstream's own call count for this endpoint, not ours.
1
Unique payers · 30d
Last called 2026-10-20 20:59Z
—
Upstream on-chain volume
Reported by the source catalog.
Paid to
0xb531320805C5BED1D46AEaDcF4F008FDF172DBDaThe wallet the 402 directs payment to. Its whole payment record — every payer, every chain — is on the merchant page.
Asset 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913
Provider
The payTo wallet does not resolve to a registered ERC-8004 agent. That is not a verdict on the service — most of the catalog is unregistered.
Live 402 challenge
Captured by the enrichment pass, not read just now. Prices can change — always read the 402 the endpoint answers with.
{
"error": "Payment required",
"accepts": [
{
"asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
"extra": {
"name": "USD Coin",
"version": "2"
},
"payTo": "0xb531320805C5BED1D46AEaDcF4F008FDF172DBDa",
"scheme": "exact",
"network": "base",
"mimeType": "application/json",
"resource": "https://css-design-calc.x402tookit.com/line-length",
"description": "Estimate characters per line from column width and font size and rate it for readability (45-75 ideal, WCAG max 80).",
"outputSchema": {
"input": {
"type": "http",
"method": "GET",
"queryParams": {
"widthPx": 720,
"fontSizePx": 18,
"avgCharWidthEm": 0.5
}
},
"output": {
"asOf": "2026-10-11T14:32:44.449Z",
"source": "Bringhurst's 45 to 75 character guideline (66 ideal) and WCAG 2.2 criterion 1.4.8 (80 characters), with the estimate computed locally",
"reasons": [
"Within the usual 45 to 75 range (66 is the classic ideal).",
"An estimate: set max-width in ch units so the browser measures the real font."
],
"summary": "About 80 characters per line (720px column, 18px type, 0.5em average glyph): long.",
"verdict": "LONG",
"widthPx": 720,
"degraded": false,
"disclaimer": "Screening signal computed from the named public source. Not financial, legal or investment advice; provided as is. Verify at the source before acting.",
"fontSizePx": 18,
"notChecked": [
"the real font: characters per line varies with the typeface, language and text (CJK counts characters, not words)",
"multi-column text, where 40 to 50 characters is acceptable",
"…2 more"
],
"suggestedCss": "max-width: 66ch;",
"widthFor45Px": 405,
"widthFor66Em": 33,
"widthFor66Px": 594,
"widthFor75Px": 675,
"widthFor80Px": 720,
"withinWcagAaa": true,
"avgCharWidthEm": 0.5,
"wcagAaaLineLimit": 80,
"charactersPerLine": 80,
"minimumLineHeight": 1.5,
"wcagTextSpacingOverridePx": {
"lineHeight": 27,
"wordSpacing": 2.88,
"letterSpacing": 2.16,
"paragraphSpacing": 36
},
"minimumParagraphSpacingMultipleOfLineSpacing": 1.5
}
},
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"scheme": "exact",
"network": "solana",
"mimeType": "application/json",
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"description": "Estimate characters per line from column width and font size and rate it for readability (45-75 ideal, WCAG max 80).",
"outputSchema": {
"input": {
"type": "http",
"method": "GET",
"queryParams": {
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"fontSizePx": 18,
"avgCharWidthEm": 0.5
}
},
"output": {
"asOf": "2026-10-11T14:32:44.449Z",
"source": "Bringhurst's 45 to 75 character guideline (66 ideal) and WCAG 2.2 criterion 1.4.8 (80 characters), with the estimate computed locally",
"reasons": [
"Within the usual 45 to 75 range (66 is the classic ideal).",
"An estimate: set max-width in ch units so the browser measures the real font."
],
"summary": "About 80 characters per line (720px column, 18px type, 0.5em average glyph): long.",
"verdict": "LONG",
"widthPx": 720,
"degraded": false,
"disclaimer": "Screening signal computed from the named public source. Not financial, legal or investment advice; provided as is. Verify at the source before acting.",
"fontSizePx": 18,
"notChecked": [
"the real font: characters per line varies with the typeface, language and text (CJK counts characters, not words)",
"multi-column text, where 40 to 50 characters is acceptable",
"…2 more"
],
"suggestedCss": "max-width: 66ch;",
"widthFor45Px": 405,
"widthFor66Em": 33,
"widthFor66Px": 594,
"widthFor75Px": 675,
"widthFor80Px": 720,
"withinWcagAaa": true,
"avgCharWidthEm": 0.5,
"wcagAaaLineLimit": 80,
"charactersPerLine": 80,
"minimumLineHeight": 1.5,
"wcagTextSpacingOverridePx": {
"lineHeight": 27,
"wordSpacing": 2.88,
"letterSpacing": 2.16,
"paragraphSpacing": 36
},
"minimumParagraphSpacingMultipleOfLineSpacing": 1.5
}
},
"maxAmountRequired": "20000",
"maxTimeoutSeconds": 300
},
{
"asset": "0x3c499c542cEF5E3811e1192ce70d8cC03d5c3359",
"extra": {
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"payTo": "0xb531320805C5BED1D46AEaDcF4F008FDF172DBDa",
"scheme": "exact",
"network": "polygon",
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"description": "Estimate characters per line from column width and font size and rate it for readability (45-75 ideal, WCAG max 80).",
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"method": "GET",
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"output": {
"asOf": "2026-10-11T14:32:44.449Z",
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"reasons": [
"Within the usual 45 to 75 range (66 is the classic ideal).",
"An estimate: set max-width in ch units so the browser measures the real font."
],
"summary": "About 80 characters per line (720px column, 18px type, 0.5em average glyph): long.",
"verdict": "LONG",
"widthPx": 720,
"degraded": false,
"disclaimer": "Screening signal computed from the named public source. Not financial, legal or investment advice; provided as is. Verify at the source before acting.",
"fontSizePx": 18,
"notChecked": [
"the real font: characters per line varies with the typeface, language and text (CJK counts characters, not words)",
"multi-column text, where 40 to 50 characters is acceptable",
"…2 more"
],
"suggestedCss": "max-width: 66ch;",
"widthFor45Px": 405,
"widthFor66Em": 33,
"widthFor66Px": 594,
"widthFor75Px": 675,
"widthFor80Px": 720,
"withinWcagAaa": true,
"avgCharWidthEm": 0.5,
"wcagAaaLineLimit": 80,
"charactersPerLine": 80,
"minimumLineHeight": 1.5,
"wcagTextSpacingOverridePx": {
"lineHeight": 27,
"wordSpacing": 2.88,
"letterSpacing": 2.16,
"paragraphSpacing": 36
},
"minimumParagraphSpacingMultipleOfLineSpacing": 1.5
}
},
"maxAmountRequired": "20000",
"maxTimeoutSeconds": 300
}
],
"x402Version": 1,
"alsoAvailable": {
"llms": "https://css-design-calc.x402tookit.com/llms.txt",
"catalog": "https://css-design-calc.x402tookit.com/catalog",
"message": "CSS Design Calc has 12 pay-per-call endpoints (CSS and layout maths for agents: unit conversion, fluid clamp(), type scales, aspect ratios, grids, specificity and readability.), from $0.02 a call. See the full menu and send your agents our way.",
"openapi": "https://css-design-calc.x402tookit.com/openapi.json",
"related": [
{
"url": "https://css-design-calc.x402tookit.com/target-size",
"path": "/target-size",
"what": "Check a click or touch target against WCAG 2.2 target size (24 px AA, 44 px AAA) includin…",
"price": "$0.02"
},
{
"url": "https://css-design-calc.x402tookit.com/type-scale",
"path": "/type-scale",
"what": "Modular type scale: sizes in px and rem for steps below and above a base size, by named r…",
"price": "$0.02"
},
{
"url": "https://css-design-calc.x402tookit.com/vertical-rhythm",
"path": "/vertical-rhythm",
"what": "Snap line-heights for font sizes to a baseline grid: baseline unit, lines per element, un…",
"price": "$0.02"
}
]
}
}Accepts
The payment requirements as published to the catalog. Read the live 402 before paying — a price here is a claim, not a quote.
0.02USDC≈ $0.02 USD
on Base · exact scheme
Pay 0.02 USDC on Base to 0xb531…2DBDa. The signed payment is good for 5 minutes.
- Paid to
- 0xb531…2DBDa
- USD Coin contract
- 0x8335…02913
- Payment window
- 5 minutes
- As published
- 20000 smallest units
20000units
on solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp · exact scheme
That figure is in the token’s smallest units. Roundhouse does not hold this contract’s decimals, so it is shown as published rather than converted.
- Paid to
- DUPiup…eEm8s
- Token contract
- EPjFWd…TDt1v
- Payment window
- 5 minutes
20000units
on Polygon · exact scheme
That figure is in the token’s smallest units. Roundhouse does not hold this contract’s decimals, so it is shown as published rather than converted.
- Paid to
- 0xb531…2DBDa
- Token contract
- 0x3c49…c3359
- Payment window
- 5 minutes
20000units
on Arbitrum · exact scheme
That figure is in the token’s smallest units. Roundhouse does not hold this contract’s decimals, so it is shown as published rather than converted.
- Paid to
- 0xb531…2DBDa
- Token contract
- 0xaf88…e5831
- Payment window
- 5 minutes
The catalog’s raw entry
[
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"scheme": "exact",
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{
"asset": "0xaf88d065e77c8cC2239327C5EDb3A432268e5831",
"extra": {
"name": "USD Coin",
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"payTo": "0xb531320805C5BED1D46AEaDcF4F008FDF172DBDa",
"amount": "20000",
"scheme": "exact",
"network": "eip155:42161",
"maxTimeoutSeconds": 300
}
]Extensions
{
"bazaar": {
"info": {
"input": {
"type": "http",
"method": "GET",
"queryParams": {
"widthPx": 720,
"fontSizePx": 18,
"avgCharWidthEm": 0.5
}
},
"output": {
"type": "json",
"example": {
"asOf": "2026-10-11T14:32:44.449Z",
"source": "Bringhurst's 45 to 75 character guideline (66 ideal) and WCAG 2.2 criterion 1.4.8 (80 characters), with the estimate computed locally",
"reasons": [
"Within the usual 45 to 75 range (66 is the classic ideal).",
"An estimate: set max-width in ch units so the browser measures the real font."
],
"summary": "About 80 characters per line (720px column, 18px type, 0.5em average glyph): long.",
"verdict": "LONG",
"widthPx": 720,
"degraded": false,
"disclaimer": "Screening signal computed from the named public source. Not financial, legal or investment advice; provided as is. Verify at the source before acting.",
"fontSizePx": 18,
"notChecked": [
"the real font: characters per line varies with the typeface, language and text (CJK counts characters, not words)",
"multi-column text, where 40 to 50 characters is acceptable",
"…2 more"
],
"suggestedCss": "max-width: 66ch;",
"widthFor45Px": 405,
"widthFor66Em": 33,
"widthFor66Px": 594,
"widthFor75Px": 675,
"widthFor80Px": 720,
"withinWcagAaa": true,
"avgCharWidthEm": 0.5,
"wcagAaaLineLimit": 80,
"charactersPerLine": 80,
"minimumLineHeight": 1.5,
"wcagTextSpacingOverridePx": {
"lineHeight": 27,
"wordSpacing": 2.88,
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"paragraphSpacing": 36
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"minimumParagraphSpacingMultipleOfLineSpacing": 1.5
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"type": "object",
"required": [
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],
"properties": {
"widthPx": {
"type": "number",
"description": "Text column width in px"
},
"fontSizePx": {
"type": "number",
"description": "Font size in px"
},
"avgCharWidthEm": {
"type": "number",
"description": "Average character width in em; 0.5 is typical for Latin text (default 0.5; 0.45 condensed, 0.55 wide)"
}
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}
},
"additionalProperties": false
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"wordSpacing": {
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"paragraphSpacing": {
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}
}Provenance
- Seen in the source catalog
- 2026-10-20 20:59Z
- Last indexed by Roundhouse
- 2026-10-22 06:50Z
- Last enriched (probe, favicon, geo)
- 2026-10-20 22:15Z
- x402 version
- 2
- Max timeout
- 300s
- Liveness probe
- HTTP 402
Hand this page to an agent
Copy the prompt and paste it into Claude, an MCP client or your own agent — it will vet this service and call it over the free read API. No key, no account.
GET api.roundhouseai.io/v0/endpoints
This endpoint's own trailing-30-day call count, as published by the upstream catalog and snapshotted daily. 4 snapshots so far. Verified volume counts only settlements with an on-chain EIP-3009 marker.
Show the promptHide the prompt
Using Roundhouse, look up the x402 service CSS Design Calc and tell me whether it is worth paying: what a call costs, whether the endpoint answered when last probed, and what its payment record actually shows. curl -s 'https://api.roundhouseai.io/v0/endpoints?q=CSS%20Design%20Calc' curl -s 'https://api.roundhouseai.io/v0/merchants/<the payTo wallet returned above>' Then call it: read the price from the live 402 at https://css-design-calc.x402tookit.com/line-length, never from a cached figure, and pay with an x402 client. The /v0 API needs an API key (`authorization: Bearer rh_live_…`) on everything except /v0/unified* and /v0/endpoints. Either pay over x402 (mint a personal key for $0.01 at GET https://api.roundhouseai.io/v0/test/x402), or ask me for an organization key, which I create at https://roundhouseai.io/dashboard/connections. If you have neither, ask before going further. If you do not have Roundhouse tools or skills installed, read https://roundhouseai.io/skill.md first — it is the whole procedure.