Free Tools API

The free tools on postboost.co are also an API. Every tool below runs the same code as its web page, so the API, the SDKs, the MCP server and the page give the same answer.

• No account needed. Call a tool without a token. With any PostBoost API token you get higher limits.
• One base URL: https://postboost.co/app/api, the same as the rest of the API.
• Catalog: GET https://postboost.co/app/api/tools lists every tool with its operation_id, web page and docs page.
• MCP: https://postboost.co/mcp/tools serves one MCP tool per free tool, no token needed. See MCP Server.

Start with the Quickstart.

Tools

Tool	operationId	MCP tool	What it does
Social media character counter	countCharacters	count-characters	Count characters as each network counts them
Social media post checker	checkPost	check-post	Check a post against each network's publishing rules
X thread maker	splitThread	split-thread	Split long text into a thread
LinkedIn post formatter	formatLinkedInPost	format-linked-in-post	Format a LinkedIn post with bold, italic and lists
Social media post preview	previewPost	preview-post	Preview where a post folds and when its image is cropped on Instagram, X, LinkedIn and Facebook
Instagram font generator	generateFancyText	generate-fancy-text	Convert text to fancy Unicode styles
AI text cleaner	cleanText	clean-text	Clean AI-written text: dashes, quotes, invisible characters, markdown
Instagram line break generator	formatInstagramCaption	format-instagram-caption	Keep blank lines in an Instagram caption with spacer lines, and count it
Post readability checker	checkReadability	check-readability	Check the readability of a post: Flesch scores, long sentences and passive hints
Emoji picker	searchEmoji	search-emoji	Search emoji by name or keyword, to copy and paste into a post
UTM builder	buildUtmUrl	build-utm-url	Build a UTM-tagged campaign URL
QR code generator	generateQrCode	generate-qr-code	Generate a QR code (SVG) for a link or text, with optional UTM tags
Link preview checker (Open Graph)	checkLinkPreview	check-link-preview	Check how a link previews on X, LinkedIn, Facebook and chat apps (Open Graph and Twitter card tags)
Engagement rate calculator	calculateEngagementRate	calculate-engagement-rate	Calculate an engagement rate
Social media ROI calculator	calculateSocialRoi	calculate-social-roi	Calculate social media ROI
Influencer rate calculator	calculateInfluencerRate	calculate-influencer-rate	Estimate an influencer's rate for one sponsored deliverable
Social media image sizes,	getImageSizes	get-image-sizes	Get social media image sizes per network, each with its source
Calculate crop	calculateCrop	calculate-crop	Calculate the crop box that fits an image to a social media size
Social media video sizes and lengths cheat sheet	getVideoSpecs	get-video-specs	Get social media video ratios, resolutions, lengths and file size limits per network, with sources
YouTube thumbnail size checker	checkYoutubeThumbnail	check-youtube-thumbnail	Check a YouTube thumbnail's ratio, width, file size and format against YouTube's requirements
Aspect ratio calculator	calculateAspectRatio	calculate-aspect-ratio	Calculate an aspect ratio, or the missing side of an image at a given ratio
Instagram carousel splitter	calculateCarouselSlices	calculate-carousel-slices	Split a wide image into seamless Instagram carousel slides
TikTok, Reels and Shorts safe zone checker	getSafeZones	get-safe-zones	Get the TikTok, Instagram Reels or YouTube Shorts safe zones for a vertical frame
Social media agent skill builder	buildAgentSkill	build-agent-skill	Build a SKILL.md, AGENTS.md or system prompt for a social media agent
X API cost calculator	calculateXApiCost	calculate-x-api-cost	Calculate the monthly X API cost
Best time to post on social media, by network and weekday	getBestTimesToPost	get-best-times-to-post	Get the best times to post per network from published studies, with sources
Social media content calendar generator	planContentCalendar	plan-content-calendar	Plan a social media content calendar and get it as CSV and ICS
Social media holiday calendar 2026-2027	listAwarenessDays	list-awareness-days	List public holidays, awareness days and social media days by date, country, type and topic, with sources
Posting frequency planner	planPostingFrequency	plan-posting-frequency	Plan how often to post on each network
Free social media audit template and scorecard	scoreSocialAudit	score-social-audit	Score a social media audit checklist and get the top fixes
Social media tool picker	pickSocialMediaTool	pick-social-media-tool	Match your needs against social media management tools and see what each one misses
Instagram hashtag generator	generateHashtags	generate-hashtags	Generate hashtags for a post topic with AI (needs a token, spends AI credits)
Instagram caption generator	generateCaption	generate-caption	Write three post captions for a topic with AI (needs a token, spends AI credits)
Hook generator	generateHooks	generate-hooks	Generate hooks (opening lines) for a social media post with AI (needs a token, spends AI credits)
Get hook templates	getHookTemplates	get-hook-templates	Get free hook templates for social media posts, filtered by style and network
Blog to social media post generator	generateSocialPostsFromBlog	generate-social-posts-from-blog	Turn a blog post (URL or text) into one social post per network with AI (needs a token, spends AI credits)
Social media manager pricing calculator	calculateSmmPricing	calculate-smm-pricing	Estimate social media manager pricing
Webhook signature verifier (HMAC)	verifyWebhookSignature	verify-webhook-signature	Verify an HMAC webhook signature
Instagram bio generator	generateBio	generate-bio	Write five profile bios with AI (needs a token, spends AI credits)
YouTube title generator	generateYoutubeTitles	generate-youtube-titles	Write five YouTube video titles with AI (needs a token, spends AI credits)
LinkedIn headline generator	generateLinkedInHeadline	generate-linked-in-headline	Write five LinkedIn profile headlines with AI (needs a token, spends AI credits)
YouTube description generator	generateYoutubeDescription	generate-youtube-description	Write three YouTube video descriptions with AI (needs a token, spends AI credits)
Social media username generator	generateUsernames	generate-usernames	Generate social media usernames
Social media glossary	getGlossary	get-glossary	Look up social media terms: plain-language definitions by category, with sources and related terms
Alt text generator	generateAltText	generate-alt-text	Write alt text for an image with AI (needs a token, spends AI credits)
Free social media report generator	summarizeReport	summarize-report	Summarize social media post metrics into a report
Hashtag group builder	buildHashtagGroups	build-hashtag-groups	Clean, dedupe and split hashtags into groups that fit a network's hashtag cap
Social media automation recipes	findAutomationRecipes	find-automation-recipes	Find n8n, Zapier and Make recipes that automate social media posting through the PostBoost API
Cross-post formatter	formatCrossPost	format-cross-post	Format one post for X, Threads, Bluesky, Mastodon and LinkedIn
Giveaway comment picker	pickGiveawayWinners	pick-giveaway-winners	Pick giveaway winners with a draw anyone can verify

Limits

Guests are counted per IP address (IPv6 per /64), token users per user. Days are UTC days.

Caller	Per minute	Per day
No token	30	500
Token, Free plan	300	1,000
Token, paid plan	300	no cap

Tools that fetch a URL have their own daily limit: 20 calls without a token, 200 with one.

Every response carries X-RateLimit-Limit and X-RateLimit-Remaining for the window closest to running out. A 429 adds Retry-After, and its body has retry_after plus register_url (no token) or upgrade_url (Free plan daily cap).

Errors

Status	When
401	The Authorization header holds an invalid token. Leave it out to call as a guest.
413	The JSON body is larger than 128 KB.
422	A field is invalid; the body lists the errors per field.
429	A limit is reached; see limits.