Cosign is a directory of people and companies built around who believes in them - and why. It helps you discover people worth working with, companies worth paying attention to, and opportunities you might otherwise miss.
You can also put your own reputation behind people and companies you believe in. Those cosigns give others useful context and help good work get recognized.
Some of the most useful knowledge in the startup world lives in people's heads: who is exceptional at their work, who made a company successful, and who is worth taking a chance on. It gets shared in introductions, group chats, reference calls, and thoughtful posts that soon disappear from the feed.
We built Cosign to give that belief a lasting, useful home. A résumé tells you where someone worked. A cosign can tell you what they contributed, why someone trusts them, and what makes them worth knowing.
We want more people to benefit from that knowledge, including those who haven't yet built a large audience or an established network.
It's getting easier to build products, start companies, and put work into the world. It's also getting harder to know where to focus your attention.
That makes human judgment more valuable. Knowing who believes in someone, and what that belief is based on, can help you find something promising before it's obvious to everyone.
People building, joining, backing, and contributing to the startup community. That includes founders and investors, but also the engineers, designers, operators, researchers, and others whose work makes companies possible.
You don't need to be well known, raising money, or looking for a job. You might be here to recognize a colleague, discover a company, find a collaborator, or keep track of people you'd love to work with someday.
Cosign is a free product from a16z. We think of it as a media drop: something useful we're putting into the ecosystem to help people discover one another, create new connections, and manufacture serendipity.
The idea is simple: more people should be able to benefit from the knowledge and relationships that help this community work. We're inviting people to build that resource with us.
It means you believe in them enough to put your name and reputation behind that belief. You're telling other people: this is someone I feel confident about, and here's why.
A cosign should carry weight. Give it thoughtfully, when you really mean it. The best cosigns make clear what you believe in: someone's ability, judgment, contribution, or potential.
Because your belief can be useful to them—and to people who haven't met them yet. It can give someone a reason to look at their work, take a meeting, or consider an opportunity together.
It also makes your judgment visible. The people and companies you choose to back say something about what you value and what you're good at recognizing. Over time, your cosigns become a useful record of the people you've believed in and the work you've helped others discover.
Because helping someone succeed can create more opportunity for both of you. If you believe in a person early, your support might help them meet a cofounder, find a role, or get their first customers. You may play a part in what they go on to build.
That's the positive-sum idea behind Cosign: your support can help create opportunities that wouldn't otherwise exist. People remember those who believed in them early. A cosign is a way to help create that future, and the relationships and reputation you build by helping people can matter for years.
The important thing is that your conviction is genuine and you can explain its basis. Working together can give you a strong reason to cosign someone. So can closely following work that gives you real confidence in their ability or potential.
Be specific about what you know. “We built our first product together” and “I've followed her research for two years” communicate different kinds of belief. Don't imply a relationship or experience you haven't had.
Tell people what you're putting your reputation behind, and give them a reason to understand your confidence. A specific contribution, a moment you saw someone's judgment at work, or a clear account of their strengths is more useful than a generic compliment.
For example: “We worked together on our first launch. She turned a confusing product into something customers understood, and I'd work with her again.”
Yes. Cosigning is the broader act of putting your name behind something you believe in. A thoughtful public list can do that at a glance; a written cosign gives you room to explain why.
The framing matters. “People I'd work with again” communicates a different judgment from “Researchers whose work I recommend.” Be clear about what inclusion means, and add context where it helps.
Someone who hasn't met you can see that a person they trust believes in you—and why. That gives them a fuller picture of you and helps your contributions travel beyond your current team, your job title, or the people who already know you.
A cosign can also give you useful context to share when meeting someone new. It isn't a promise of an introduction or an opportunity, but it can help someone understand why they should take a closer look.
We want a place where people celebrate good work and help others move forward. Building something is hard, and many of the people who make it happen get little public recognition.
Positive doesn't have to mean indiscriminate. An endorsement matters because someone chooses to attach their name to it. Read who is saying what, and why. Having few or no cosigns is not a negative judgment about a person.
A follow can mean you're curious about someone's posts. A connection can mean anything from years of working together to a brief encounter.
Cosign is built around a more specific question: what do you believe about this person or company, and why? It brings that context together on profiles and lists so other people can find it when it's useful, long after the original post or conversation.
Start with a person, company, or question you care about. Explore a list, follow it to a profile, and see who has put their name behind the people or companies you find there.
Then contribute something you know. Cosign someone you really believe in, make a useful list, or add context to your own profile. You don't need to build a large network before you can help someone else discover something good.
A Community list brings people together around a question, such as who they would recommend for a particular kind of work. Members contribute people or companies and cosign the responses they believe in.
The result is a shared resource that can keep getting more useful as people contribute. On ranked lists, ordering can reflect the reputation behind contributions as well as how many people have contributed. It's a starting point for discovery, not a definitive verdict on who's best.
Connect immediately adds a person to your private globe. The button then becomes Message. Companies cannot be connected; your published work experience automatically adds those companies to your globe.
Message sends a private written message to a person or company. Explain your interest in funding, hiring, working together, or anything else in your own words. A message does not add the recipient to your globe.
Cosign is public support for a person or company and adds them to your globe. A public cosign message and adding them to your lists are optional.
Start with companies recommended by people whose judgment you value. Explore why they're on a list, learn about the team and what they're building, and look at their open roles.
You can save jobs to revisit. Message opens a private conversation with a verified founder, or a company page admin when no founder is available. Apply takes you to the employer's application destination. Listings come from company job boards, so check the employer's page for current availability.
No. A useful profile, a thoughtful cosign, or a good list can keep helping people after you've contributed it. You can return when you have something to share, someone to recognize, or a question to explore.
Cosign is also for people who are happy where they are and open to the right person, idea, or opportunity.
From people contributing to Cosign and from publicly available sources. Profiles can bring together career information, company details, public announcements, attributed praise, and community activity.
Some cosigns are written directly on Cosign. Others preserve public statements made elsewhere, such as a thoughtful post on X. A sourced statement does not mean its author joined Cosign or submitted it here. Look at its source and context to understand what was said.
AI helps research and organize public information, including company information, talent moves, and public praise. The belief behind a cosign belongs to the person who expressed it.
Automated research can be incomplete or wrong. Talent Watch, Funding Watch, and similar research features are summaries of public information, not official announcements from the people or companies shown. Check the supporting sources when something matters to your decision.
Cosign can create profiles from public information and community contributions. That makes the directory useful before everyone has signed up.
A profile's existence doesn't mean the person created it or participates in Cosign. They can claim the matching profile by connecting their identity, or request a correction or removal if something is wrong or they don't want it displayed.
Company profiles bring together information about an organization, including its people, products, cosigns, and jobs. Creating a company profile adds it to the directory; it doesn't give the person who added it control of the company account.
Company representatives can request control of their company's profile.
You can edit cosigns you've written; changes may be reviewed before appearing.
If profile information is inaccurate or a statement has been attributed incorrectly, request a correction. You can contact privacy@a16z.com to request correction or removal of a profile, including one you haven't claimed. The privacy policy explains more.
Contributions may be reviewed before publication to address spam, abuse, and other content that doesn't belong on Cosign. Some submissions may need human review.
Publication doesn't mean Cosign has independently verified every claim. A cosign reflects its author's judgment; it isn't an endorsement by a16z or a guarantee about a person or company.
You can manage message, recap, and product-update emails in Email preferences. For details about your information, your content, and using Cosign, read the privacy policy, terms of use, and disclosure.
Put your name behind people and companies you genuinely believe in. Explain what makes them worth knowing. Create a list that would help someone else, contribute useful context, and tell us when something needs correcting.
We're putting Cosign into the world as an invitation to build something together. The hope is that two people meet, a team finds the person it needs, or someone discovers a company they love because another person chose to share what they knew. That's the kind of serendipity we'd like to help manufacture.