Apollo
Apollo bundles a large B2B contact database (230M+ firmographic, email, phone) with native outreach sequences, making it the default starter for teams that want data and engagement in one place. Coverage is broad but shallow compared to ZoomInfo. The generous free tier (60 mobile credits/year, unlimited email lookups with verification) makes it the go-to for solo founders and early sales teams.
Official site ↗Why it ranks here
Most teams start here because you get contact data, email sequences, and basic CRM sync without paying for three separate tools. The free tier removes the cold-start problem.
Where it sits
Apollo sits at rank 1 for new GTM teams. If you already own ZoomInfo or need deeper firmographic intelligence, Apollo becomes redundant. For single-tool simplicity, nothing beats it.
How GTM Engineering teams use it
GTM engineers pipe Apollo contacts into Clay or directly into Salesforce via native sync. Teams use Apollo for top-of-funnel list building, then export to orchestration layers (Clay, Workato) for waterfall enrichment. The engagement layer (sequences, calling) often gets replaced by Outreach or Salesloft at scale, but Apollo remains the data source.
In-depth notes
Data quality is uneven: email accuracy hovers around 85-90 percent (lower than ZoomInfo), and mobile coverage skews US. The all-in-one model is both a strength (simplicity) and a weakness (jack-of-all-trades). If you outgrow the free tier, pricing increases with paid plans. Watch your credit burn rate: mobile lookups and enrichment APIs consume credits per record.
Best for
Early-stage teams, solo founders, and GTM engineers prototyping outbound motions before investing in enterprise data stacks.
Avoid if
You need deep firmographic hierarchies, technographics, or EMEA mobile coverage (ZoomInfo and Cognism win there).
The rest of Data providers
ZoomInfo Leader Enterprise B2B data standard with 100M+ contacts, deepest US firmographics, and technographic + intent layers. #3 
Cognism Leader EMEA-focused B2B data provider with GDPR-compliant mobile coverage (Diamond Data) and strong UK/EU accuracy. #4 
Lusha Strong SMB-friendly B2B data provider with simple UI, Chrome extension, and good mid-market contact coverage. #5 
Bombora Strong B2B intent data standard (Company Surge) that tracks content consumption across 4k+ B2B sites. #8 
LeadIQ Situational Prospecting workflow tool with Chrome extension, contact data, and one-click Salesforce sync. #9 
RocketReach Situational Personal email finder with 700M+ profiles, strong coverage of executives, influencers, and passive candidates. #10 
Seamless.AI Situational Real-time contact finder with Chrome extension, strong coverage of direct dials, and aggressive UI. #11 
Hunter.io Situational Email finder and domain search tool with 100M+ email addresses, simple UI, and generous free tier. #12 
Demandbase Situational ABM platform with intent data, advertising, and account intelligence for enterprise B2B sales teams. #13 
Kaspr Niche LinkedIn Chrome extension for GDPR-compliant B2B contact data, strong in EMEA, simple UI. #14 Learning guide
Setup
Sign up for free account at apollo.io, verify email, and start searching immediately with 60 mobile credits and unlimited email lookups per year.
First thing to build
Run a job title search for your ICP (e.g., Director of Engineering at 50-500 employee SaaS companies in California), export 25 contacts, and verify email accuracy in Clay or your CRM.
What actually matters
- Set search filters: company size, industry, location, and technology stack to match your ICP before running expensive mobile lookups
- Enable email verification in export settings to reduce bounce rates (verification consumes credits but saves deliverability)
- Configure Salesforce or HubSpot native sync under Integrations to auto-push new contacts, but test field mapping on 10 records first
- Monitor credit burn in Account Settings: mobile lookups cost 1 credit, email exports are free but verification costs 0.25 credits per email
Watch out
Free tier mobile credits expire after one year and do not roll over; if you burn all 60 in the first month on low-fit prospects, you will hit a paywall before validating your ICP.