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Developer Tools · head to head

ConfigCat vs Nessus

ConfigCat logo

ConfigCat

Developer Tools

Feature flag service priced per flag and environment with unlimited seats and unlimited monthly active users

From
Free
Free plan
Yes
Full reviewWebsite
Nessus logo

Nessus

Cybersecurity

The most trusted vulnerability assessment solution

From
$4790/year
Free plan
No
Full reviewWebsite

The short version

  • Only ConfigCat has a free tier, so it costs nothing to try first.
  • Each has a real cost: ConfigCat there is no experimentation or statistical analysis engine, so teams wanting real A/B tests with significance testing must buy and integrate a separate analytics or experimentation product.; Nessus nessus Professional is $4,790 for one year, with no free or low cost commercial tier
  • They diverge on capability: ConfigCat covers Feature flags and configuration, Nessus covers Vulnerability scanning.
  • Prices and features above were last checked on 31 August 2026.

Where they differ

Only the attributes on which ConfigCat and Nessus actually diverge.

Attributes where ConfigCat and Nessus differ
AttributeConfigCatNessus
Starting priceFree$4790/year
Pricing modelPer month by feature flag and environment countsubscription
Free tierYesNo
PlatformsWeb, API, iOS, Android, Node.js, .NET, Java, Python, GoDesktop, Api
CategoryDeveloper ToolsCybersecurity
FoundedUnknown2002

Identical on both: user rating (Not yet rated).

What each one covers

Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.

Only in ConfigCat

  • Feature flags and configuration
  • Percentage rollouts
  • Targeting rules and segments
  • Unlimited seats
  • Global CDN delivery
  • Audit log
  • Public API and webhooks
  • SDKs across languages

Only in Nessus

  • Vulnerability scanning
  • Configuration auditing
  • Malware detection
  • Web application scanning
  • Cloud scanning
  • Compliance checks
  • Patch auditing
  • Pre-built policies

What people use each for

The jobs each tool is most often brought in to do.

ConfigCat

  • A consumer or mobile app with millions of users where per-MAU flag pricing would cost more than the flags are worthnot Nessus
  • A team that wants every engineer, product manager and support agent to have a login without paying per seatnot Nessus
  • Decoupling deployment from release with percentage rollouts and a kill switch, without buying an experimentation platformnot Nessus
  • A small team that needs ten flags permanently and can run indefinitely on the free tiernot Nessus

Nessus

  • Vulnerability scanning for individual practitionersnot ConfigCat
  • Enterprise vulnerability managementnot ConfigCat
  • Web application security assessmentsnot ConfigCat

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

ConfigCat

  • There is no experimentation or statistical analysis engine, so teams wanting real A/B tests with significance testing must buy and integrate a separate analytics or experimentation product.
  • Pricing by flag count punishes exactly the hygiene you want: the Pro tier caps at 100 flags, so teams that do not aggressively retire stale flags are pushed to the 325 dollar Smart tier for housekeeping reasons rather than growth.
  • The free tier allows only 2 environments, which does not cover the common development, staging and production split, so almost any real deployment starts on a paid plan.
  • It is a smaller vendor than the category incumbents, so enterprise procurement teams will find less depth in compliance attestations, contractual terms and reference architecture than LaunchDarkly offers.
  • Flag evaluation relies on SDK-side caching of a CDN-delivered config, which is fast but means propagation of a change is eventually consistent rather than instant, something to understand before relying on it as an emergency kill switch.

Nessus

  • Nessus Professional is $4,790 for one year, with no free or low cost commercial tier
  • Multi year terms are the only discount route, at $9,330.95 for two years and $13,637.54 for three
  • It is a single user scanner, so team workflows mean migrating to another Tenable product
  • Tenable One vulnerability management is priced separately, starting at $3,500 a year for 100 assets

Pricing, plan by plan

ConfigCat

Free
  • Forever FreeFree
    • 10 feature flags
    • 2 environments and 2 products
    • 2 segments
  • Pro$110/month
    • 100 feature flags
    • 3 environments and 3 products
    • Unlimited seats and MAUs
  • Smart$325/month
    • Unlimited feature flags
    • Unlimited environments, products and segments
    • Unlimited seats and MAUs
  • Enterprise$900/month
    • Everything in Smart
    • Enterprise support and controls
    • Unlimited everything on flag counts

Nessus

$4790/year
  • Nessus Professional$4790/year
    • 1 year license
    • Best for individual security professionals
  • Nessus Professional 2-Year$9330.95/2 years
    • 2 year license with discounted rate vs. annual
  • Nessus Professional 3-Year$13637.54/3 years
    • 3 year license with discounted rate vs. annual
  • Nessus Expert$6790/year
    • 1 year license
    • Enhanced capabilities vs. Professional

Which should you pick?

Choose ConfigCat if

  • You need feature flags and configuration.
  • You want to start without paying.
  • You work on Web, API, iOS, Android, Node.js, .NET, Java, Python, Go.
  • You also want percentage rollouts.
ConfigCat review

Choose Nessus if

  • You need vulnerability scanning.
  • You work on Desktop, Api.
  • You also want configuration auditing.
Nessus review

Questions people ask

Is ConfigCat or Nessus better?
Neither clearly leads. ConfigCat starts at Free and Nessus at $4790/year, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, ConfigCat or Nessus?
ConfigCat has a free tier; the other does not. Paid plans start at Free for ConfigCat and $4790/year for Nessus.
Does ConfigCat or Nessus run on more platforms?
ConfigCat runs on Web, API, iOS, Android, Node.js, .NET, Java, Python, Go. Nessus runs on Desktop, Api.
Can I use ConfigCat for free?
Yes. ConfigCat has a free tier, so you can try it without paying. Nessus starts at $4790/year.
What is ConfigCat best used for?
ConfigCat is most often used for a consumer or mobile app with millions of users where per-mau flag pricing would cost more than the flags are worth, a team that wants every engineer, product manager and support agent to have a login without paying per seat, decoupling deployment from release with percentage rollouts and a kill switch, without buying an experimentation platform, a small team that needs ten flags permanently and can run indefinitely on the free tier. Of those, a consumer or mobile app with millions of users where per-mau flag pricing would cost more than the flags are worth and a team that wants every engineer, product manager and support agent to have a login without paying per seat are not what Nessus is typically brought in for.
What can ConfigCat do that Nessus cannot?
ConfigCat covers Feature flags and configuration, Percentage rollouts, Targeting rules and segments, Unlimited seats. Nessus covers Vulnerability scanning, Configuration auditing, Malware detection, Web application scanning.

Answered from the vendors’ own pages

ConfigCat: How is ConfigCat priced?

By feature flag, environment and product count. Seats, monthly active users and flag reads are unlimited on every plan.

Nessus: What is the cheapest Nessus option?

Nessus Professional starts at $4,790 per year for a 1-year license. Multi-year commitments offer discounts, with 2-year licenses at $9,330.95 and 3-year licenses at $13,637.54.

Source
ConfigCat: Is the free tier usable?

For small projects yes, but at 10 flags and 2 environments it will not cover a dev, staging and production setup.

Nessus: What is the difference between Nessus Professional and Expert?

Nessus Expert costs $6,790 per year for a 1-year license (compared to $4,790 for Professional) and includes enhanced capabilities. Multi-year rates are available at discounted prices.

Source
ConfigCat: Can it run A/B tests?

It can split traffic, but there is no statistics engine. You need a separate analytics tool to decide a winner.

Nessus: Does Nessus offer optional support or training?

Yes, Nessus offers add-on services: Advanced Support at $400/year provides 24x365 access to phone, email, community, and chat support. On-Demand Training costs $275/year for Fundamentals course access or $385/year for both Fundamentals and Advanced courses.

Source
ConfigCat: How fast does a flag change take effect?

SDKs poll and cache, so changes propagate on the polling interval rather than instantly.

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