This is the stack for the technical screen — the stretch between “the resume looks right” and “four engineers spent an afternoon on an onsite.” It assumes you already have recruiters and an ATS, and that your constraint is engineering hours, not applicant volume.
Two things changed the shape of that screen. Candidates now use AI assistants while they answer, so a test that measures unassisted recall measures a skill nobody will use on the job. And identity stopped being free: the U.S. Justice Department’s January 2025 indictment in the North Korean remote-IT-worker scheme found that over 300 U.S. companies, several of them Fortune 500, had unknowingly hired workers operating under false identities. A screening pipeline designed before either of those is scoring the wrong thing and verifying nothing.
The stack answers both with four layers: one async assessment platform that narrows the funnel cheaply — CodeSignal or HackerRank, not both — Karat for the live screen you do not staff, and Greenhouse as the identity gate and the structured record everything writes back to.
If you want the whole hiring loop rather than the technical screen specifically, that is the AI-augmented recruiting stack. This one goes deep on one step.
How the pieces fit
- CodeSignal is the calibrated async filter. Its Coding Score is a 600-850 scale built to be comparable across candidates and across reqs, which is what turns a screen result into a number a hiring manager can argue with. The Hire plans meter on credits and include AI Interviewers and AI Proctoring with ID verification from the entry tier up. The buying detail that decides the tier: ATS integrations start at the Grow plan, so the $79/mo entry tier writes nothing to Greenhouse and a recruiter copies results by hand.
- HackerRank is the same layer with a wider question library and published overage. It carries thousands of pre-calibrated problems across 35+ languages, which removes the question-authoring load that otherwise falls on your staff engineers. Its AI interviewer, Chakra, scores on a 5-point scale at overall and section level and returns bullet summaries with transcript references and audio playback, and it integrates with Greenhouse and Ashby directly. Pick it over CodeSignal when your volume is spiky and you want a stated overage rate rather than a renegotiation.
- Karat is the live technical screen you do not staff. Its network of trained Interview Engineers runs the 45-60 minute screen on your behalf, 24/7, and returns a scored written report against a fixed rubric. Its NextGen Interviews format, launched 10 December 2025, puts an AI assistant inside the interview on a multi-file project and has the Interview Engineer probe the candidate’s reasoning while they use it — the assessment is how well the candidate directs AI under pressure, which is the thing an async proctored test is structurally unable to measure. Karat also absorbed Byteboard’s assessment technology in January 2025, its third acquisition in two years.
- Greenhouse is the system of record and the identity gate. Scorecards and interview kits are first-class, which is what makes the assessment results comparable rather than filed. Its Real Talent suite carries the verification layer: fraud detection runs a candidate’s phone, email, IP address and location through IPQualityScore and returns 26 signals grouped into high-risk, moderate and authenticity markers, and identity verification is a CLEAR selfie check inside the candidate’s MyGreenhouse profile. Both sit in the Plus and Pro tiers — on Core you have the ATS but not the identity gate, and that single line decides whether this stack does the job you bought it for.
The handoffs that make it a stack
Each arrow is an event, not a habit.
An application lands in Greenhouse. Real Talent fraud detection scores it on application signals before a recruiter opens it, and high-risk signals route to manual review rather than to auto-reject — the signals are rules over phone, email, IP and location, not a model verdict on the person. Candidates who clear go to the async assessment: Greenhouse triggers the CodeSignal or HackerRank invite from the stage transition, and the returned score writes back onto the candidate record. A score above your cut line advances the candidate to Karat, which is booked from the same stage and returns a scored report and a pass/fail into Greenhouse within hours rather than after a scheduling round-trip. A Karat pass triggers the CLEAR identity check before the onsite is scheduled — the last cheap moment to confirm the person who passed the screen is the person who will show up. The onsite runs against Greenhouse scorecards, and stage-conversion reporting closes the loop: if 80% of candidates who clear the async assessment fail the Karat screen, the cut line is wrong, not the candidates.
Why this combination
Because a technical screen has three failure modes and no single vendor covers all three. An async test scales but cannot tell a strong engineer from a strong prompter. A human interview reads judgment but costs engineering hours you are trying to protect. And neither one verifies identity — that is an ATS-layer job because it has to happen on the application record, before anyone spends a credit or an interview slot.
The load-bearing rule: one assessment vendor, one ATS, and the ATS owns the trigger. Running CodeSignal and HackerRank side by side gives you two incomparable scores on the same funnel and two renewals, and the Coding Score’s whole argument is that it is comparable. Triggering assessments from the assessment tool instead of from Greenhouse gives you candidates who sit in an assessment queue that no ATS report can see. That is why the ATS tier matters more here than the assessment tier does.
What it costs
Budget $25K-$90K a year for 40-80 engineering hires, with Karat as the dominant line and the ATS quoted separately.
- CodeSignal Hire publishes $79/mo billed annually ($99 monthly) for Build with 60 annual credits, and $479/mo billed annually ($599 monthly) for Grow with 420 annual credits and basic ATS integrations. Pro is quoted and is where advanced fraud prevention and enterprise ATS integrations sit. Overage runs $20 per credit. CodeSignal does not publish what one credit buys — get that in writing before you size a plan, because the difference between a credit-per-invite and a credit-per-completion is roughly your funnel’s completion rate.
- HackerRank publishes Starter at $199/mo ($1,990/yr, so $165/mo on annual) and Pro at $449/mo ($4,490/yr, $375/mo annual), with overage at $20 per attempt or $15 pre-purchased on annual plans. Enterprise is quoted.
- Karat does not publish a rate card. Per-interview pricing runs roughly $350-$450 at low volume and $200-$280 above 2,000 interviews a year, with premium formats — system design, staff-level, NextGen — carrying a 20-40% premium. Vendr transaction data puts the median buyer contract at $175,695 a year, which tells you the shape of the customer base rather than the shape of your bill. Volume commitments are binding: commit to 500 interviews, use 300, pay for 500. Budget $5K-$25K for onboarding and rubric setup.
- Greenhouse is quoted across Core, Plus and Pro. You have it already or this is the wrong stack — but if you are on Core, the Plus upgrade is a line item this stack requires, not an optional one.
The break-even test is engineering hours. A screen you run internally costs an engineer roughly 90 minutes end to end including prep and debrief. At 300 screens a year that is 450 engineer-hours; at a $110/hr fully loaded cost, $49,500 of engineering time against roughly $105K of Karat at the $350 rate. Karat wins on hours only when your engineers are the constraint and their hours have somewhere better to go. If they don’t, run the live screen internally and buy the assessment platform alone for about $5K.
Common variations
- Assessment platform only, no Karat. Under 20 engineering hires a year the interview-as-a-service math does not close — you are paying a $200-$450 unit cost to protect hours you are not short of. Keep CodeSignal or HackerRank, run the live screen with your own engineers against a fixed rubric, and revisit when a hiring manager starts declining interview requests.
- Swap Greenhouse for Ashby. Ashby’s native analytics answer the stage-conversion question this stack depends on without a reporting upgrade, and both HackerRank and CodeSignal integrate with it. Choose it when you are selecting an ATS now rather than replacing one — but confirm the identity-verification path first, because Real Talent and the CLEAR check are Greenhouse-specific.
- Karat only, no async layer. Works when your applicant volume is small and senior-heavy and every candidate deserves a live screen. It removes the calibrated score, so hiring managers argue from interview reports instead of numbers. Swap back the moment applicant volume per req passes about 50.
- CodeSignal to HackerRank on the overage line. If you are consistently paying CodeSignal overage without knowing the credit definition, HackerRank’s published $20-per-attempt (or $15 pre-purchased) is the same money with a stated unit. Move on the renewal, not mid-term.
When this stack is the right pick — and when it isn’t
Pick it when you hire 20-200 engineers a year, your engineers are the scarce resource, at least some hiring is remote, and you already run structured hiring — structured interviewing is the precondition, not the output. It is also the right pick when someone has asked you to prove the person interviewed and the person hired are the same human, because the CLEAR and IPQualityScore layers are the only part of this stack that answers that.
Skip it in three cases. Under 20 engineering hires a year the Karat commitment and the ATS tier upgrade both fail on unit economics — buy the assessment platform and nothing else. If your hiring is high-volume hourly or frontline rather than engineering, this is the wrong category entirely; that is the high-volume recruiting stack. And if your loop has no rubric — no defined cut line, no scorecard, no agreed bar — buying assessment adds a number nobody trusts. Fix the loop with the interview loop builder first.
What this stack does NOT replace
- Sourcing. Nothing here finds candidates. The pipeline this stack filters has to arrive from somewhere — inbound, or the AI sourcing stack.
- The onsite and the hiring decision. Karat returns a pass/fail on technical ability. Architecture depth, collaboration, and role fit stay in your loop, and the debrief stays human — see interview loop design.
- Background screening. CLEAR verifies that the applicant is the person on the ID. It does not check employment history, education, or criminal record; that is a separate purchase and a separate vendor.
- Your quality-of-hire measurement. This stack produces a screen score and a conversion rate. Whether the people you hired are good at the job is measured after they start, against performance data the ATS does not hold.
- Your obligations when AI scores a candidate. Chakra and CodeSignal’s AI Interviewers rank people. Where AI-assisted evaluation feeds a hiring decision, disclosure, bias-audit and notice rules — NYC LL 144 and the EU AI Act among them — attach to the employer, not the vendor. Greenhouse states plainly that its fraud detection is rules over objective signals rather than AI scoring, which is a deliberate design choice on their side and a fact you should be able to repeat to a regulator on yours.