Overview
Reference checks are structured conversations with people who have directly worked with a candidate—typically former managers, peers, or cross-functional collaborators. While candidates provide references who will speak favorably, skilled reference checks extract valuable signal beyond surface endorsements.
The purpose isn't to catch candidates lying—it's to validate what you learned in interviews and fill gaps in your understanding. References can reveal how someone operates under pressure, collaborates across teams, handles feedback, and grows over time. They provide context interviews can't: actual performance history rather than self-reported stories.
For engineering hiring, reference checks serve a unique function: technical interviews assess current skills, but references reveal how someone learns, adapts, and works with others over sustained periods. A brilliant coder who alienates teammates looks very different to references than to interviewers.
Why Reference Checks Still Matter
Reference checks have a reputation problem. Candidates provide favorable references, legal constraints limit what references can say, and the whole process feels like a formality. Many companies skip them entirely or rush through perfunctory calls.
This is a mistake. Done well, reference checks provide signal you can't get elsewhere.
What References Reveal That Interviews Don't
Sustained performance over time. Interviews capture a snapshot—a few hours of prepared performance. References have observed the candidate over months or years. They've seen the trajectory: Did they grow? Did they plateau? Did early success give way to coasting?
Behavior under real pressure. Interview "tell me about a time" questions get rehearsed stories. References witnessed the actual moments—and remember how the candidate really responded when things went wrong, deadlines slipped, or conflicts erupted.
Impact on others. Candidates describe their own contributions. References describe what it was actually like to work with them. Did they lift the team or drain energy? Did they share credit or hog it? Did they mentor others or only focus on their own work?
Patterns across contexts. A candidate might have one great story about handling conflict. References can tell you whether that's representative or an exception. "They handled that well once" is different from "they consistently handle conflict well."
Honest development areas. Candidates give carefully hedged weaknesses in interviews. References, asked the right questions, reveal genuine growth areas—the things the candidate is actually working on, not the sanitized version.
The Validation Function
Beyond new information, references validate or challenge your interview impressions. When references confirm what you saw, your confidence increases. When there's dissonance—you loved them, references are lukewarm—that's a signal to investigate.
The validation isn't binary. Sometimes references add context that changes interpretation: "Yes, they struggled with that project, but you should know the context—the codebase was a mess, leadership kept changing requirements, and they were the only experienced person on the team."
What to Ask References
The difference between useful and useless reference checks is the questions you ask. Generic questions get generic answers. Specific, context-rich questions get signal.
The Essential Questions
"Would you hire/work with them again?" This is the single most valuable reference question. It's binary and personal—the reference has to commit. Listen carefully to how they answer. An enthusiastic "absolutely, in a heartbeat" is very different from "yes, I think so" or "it would depend on the role."
"What do I need to know to set them up for success?" This reframes "weaknesses" as helpful context. References who care about the candidate want to help them succeed—they'll share insights they might not volunteer if asked "what are their weaknesses?" You'll learn about management style preferences, team dynamics that work or don't, and areas where support helps.
"Can you describe a specific time when..." Always anchor questions to concrete situations. Instead of "are they collaborative?" ask "can you tell me about a time they had to work through a disagreement with another engineer?" Specific stories are harder to fabricate and reveal more detail.
"How did they handle [specific situation from interview]?" Use interviews to generate reference questions. If the candidate told you about a challenging project, ask the reference for their perspective. Consistent stories increase confidence; divergent accounts warrant investigation.
"What kind of work brings out their best?" This helps with role fit even for strong candidates. A backend engineer who thrives on ambiguous problems might struggle with well-defined maintenance work. Understanding what energizes them helps you assess fit and plan onboarding.
Questions by Reference Type
Former managers can tell you about:
- Performance trajectory over time
- How they responded to feedback
- Areas where they needed support
- How they compared to peers at their level
- Readiness for the next level
Former peers can tell you about:
- Day-to-day collaboration style
- How they handled disagreements
- Whether they helped others or only focused on their own work
- Technical strengths and gaps in practice
- What it was actually like to work with them
Cross-functional partners can tell you about:
- Communication with non-engineers
- How they handled competing priorities
- Reliability on commitments
- Ability to translate technical concepts
- Stakeholder management
Questions to Avoid
"Can you confirm their dates of employment?" This is HR verification, not a reference check. Don't waste limited reference time on administrative details.
"What are their weaknesses?" This generic question yields rehearsed non-answers. Ask about growth areas, what helps them succeed, or specific challenges instead.
"Are they a good person?" Subjective character assessments aren't actionable. Ask about specific behaviors and situations.
"Why did they leave?" The candidate already told you. Unless you have specific concerns, this just burns time and can make references uncomfortable.
Interpreting Reference Signals
Reference checks are conversations, not interrogations. The signal is in the details—tone, enthusiasm, hesitation, specific examples, and what's not said.
Reading Between the Lines
Enthusiastic specificity vs. generic praise. Strong references provide detailed examples and genuine enthusiasm. "They were great to work with" is polite but empty. "I still remember how they debugged that production issue at 2 AM—they stayed calm, methodical, and kept everyone updated" is meaningful.
Immediate response vs. careful hedging. When you ask "would you hire them again?" listen to the response time. An immediate "absolutely" differs from "well, it would depend on the role" or "I think so, yes."
What they emphasize vs. what you asked. If you ask about technical skills and they pivot to how nice the person is, that's interesting. If you ask about collaboration and they redirect to individual contributions, notice that.
The "but" after the praise. "They're a strong engineer, but..." often precedes the real information. Don't rush past qualifiers—explore them.
References they offer vs. references you requested. If you asked for a former manager and they provided a peer, or substituted one reference for another, ask why. There might be good reasons (manager left the company) or revealing ones (manager wouldn't say positive things).
Common Signal Patterns
Strong candidate pattern:
- References respond quickly and enthusiastically
- Specific, detailed examples come easily
- Praise is substantive, not generic
- Growth areas are acknowledged but contextualized
- Clear desire to see the candidate succeed
Weak candidate pattern:
- References are hard to reach or slow to respond
- Answers are vague or generic
- Hedging and qualification throughout
- Redirection away from direct questions
- Faint praise or damning with faint praise
Mixed candidate pattern:
- Strong in some areas, gaps in others
- Different references emphasize different things
- Context-dependent performance
- Clear growth trajectory (or decline)
The "Reference Sandwich"
References often deliver difficult information between positive statements. Listen for the middle: "They were a really strong technical contributor. There were some challenges with how they communicated with the product team. But they really grew a lot and I was sad to see them go."
The middle piece—"challenges with how they communicated with the product team"—is the signal. Follow up on it.
Common Reference Check Mistakes
Reference checks go wrong in predictable ways. Avoiding these mistakes dramatically improves signal quality.
Treating References as Formalities
The biggest mistake is not taking references seriously. Rushing through calls, asking generic questions, accepting surface-level answers—this turns reference checks into box-checking exercises that waste everyone's time.
Fix: Block adequate time, prepare specific questions, and treat reference calls as genuine information-gathering conversations.
Doing References Too Late
Many companies do reference checks after making offer decisions, treating them as final verification rather than input. By then, you're psychologically committed—you'll rationalize away concerning signals rather than changing course.
Fix: Complete reference checks before making offer decisions. They should inform the decision, not rubber-stamp it.
Only Calling Provided References
Candidates provide references they know will be positive. This is expected and fine—but recognize the limitation. For senior roles or when you have specific concerns, backchannel references (with appropriate care) provide different perspectives.
Fix: For critical hires, supplement provided references with backchannel references where you have legitimate connections.
Asking Leading Questions
"They seemed really collaborative in the interview—would you agree?" This gets affirmation, not information. You've told the reference what you want to hear.
Fix: Ask open questions that don't telegraph desired answers. "How would you describe their collaboration style?" lets the reference shape the response.
Not Following Up on Interesting Signals
When a reference says something intriguing, don't move to your next question. Probe deeper. "That's interesting—can you tell me more about that situation?" often yields the most valuable information.
Fix: Treat unexpected responses as openings, not distractions. Follow the signal.
Ignoring Disconfirming Information
When references contradict your positive interview impression, the temptation is to rationalize: maybe that reference had a personal conflict, maybe the context was unusual, maybe they're just not a good reference. Sometimes these rationalizations are correct—but sometimes you're ignoring valid signal.
Fix: Take disconfirming information seriously. Investigate further rather than explaining it away.
Backchannel References
Backchannel references—conversations with people who know the candidate but weren't provided as references—are controversial but common, especially for senior roles. Done ethically, they provide valuable perspective. Done carelessly, they violate trust and create legal risk.
When Backchannels Make Sense
Senior and executive hires. The stakes are higher, the candidate has more practice presenting well, and you likely have mutual connections who can provide perspective.
Specific concerns from interviews. If something in the interview process raised flags, backchannel references can help validate or dismiss concerns.
Industry-specific roles. In tight-knit industries (like developer tooling), people know each other. Your network likely includes people who've worked with the candidate.
Ethical Backchannel Principles
Never contact current employer without permission. This can endanger the candidate's current job. It's both unethical and potentially illegal.
Use only legitimate connections. Reaching out to strangers about a candidate crosses lines. Backchannel references should come from your genuine professional network.
Be transparent when asked. If the candidate asks whether you'll do backchannels, be honest. Some candidates appreciate it; others may have concerns you should understand.
Weight appropriately. Backchannel references are informal and unstructured. One person's negative opinion isn't conclusive—but patterns across multiple backchannels are significant.
Consider the source. Why might this backchannel reference have a particular view? Are they a reliable judge? Did they have personal conflicts with the candidate?
Conducting Backchannel References
Approach them conversationally, not as formal reference checks:
"I'm talking to [Candidate] about a role. I know you overlapped at [Company]. I'd love to hear your general impressions—what's it like working with them?"
Listen for themes that match or contradict what you've learned elsewhere. A backchannel reference doesn't need to provide specific performance data—they're providing texture and perspective.
When to Be Cautious
Small industries where word spreads. If the candidate will learn you're asking around, consider whether that damages the relationship.
When you lack appropriate connections. Don't reach out to strangers. If you don't have legitimate backchannel options, rely on provided references.
When it becomes excessive. One or two backchannel conversations for a senior role is reasonable. Extensive background investigation feels invasive and suggests distrust.
Structuring the Reference Process
A well-structured reference process improves consistency and signal quality.
Timeline
Schedule references early. Don't wait until the final interview stage. Provided references need scheduling lead time, and you want results before decision-making.
Target 2-3 references minimum. One reference is insufficient—you need multiple perspectives to see patterns. For senior roles, 3-4 references from different relationship types is ideal.
Allow 30 minutes per call. Fifteen minutes rushes the conversation. Thirty minutes allows for follow-up questions and deeper exploration.
Reference Request Process
Ask candidates for specific reference types. Rather than "provide three references," ask for "a former manager who observed your day-to-day work, a peer you collaborated closely with, and someone from another function you worked with regularly."
Get context upfront. When candidates provide references, ask them to briefly describe the relationship and time period. This helps you tailor questions.
Provide references with context. When scheduling, share the role the candidate is interviewing for. This helps references provide relevant perspective.
Documentation
Take notes during calls. Don't rely on memory—write down specific quotes and examples.
Summarize patterns across references. After completing all calls, identify themes: where do references agree? Where do they diverge? What picture emerges?
Document for defensibility. Reference check notes may be legally discoverable. Keep records factual and job-related.