Overview
Fern turned an internal-infrastructure advantage into a product smaller API companies could buy. Amazon and Palantir had built systems to generate client libraries from API definitions. Most companies still chose between hand-maintained SDKs and open-source generators that produced uneven code. Fern packaged the hard parts: language-native SDKs, synchronized documentation, publishing, enterprise controls, and eventually agent-facing interfaces.
The first customer took more than 18 months. Less than four years after founding, Fern had 25 employees, more than 200 customers, millions in annual revenue, and a January 2026 acquisition by Postman.[1] Fern stayed an independent product, and the entire team joined the buyer.[2]
This was a distribution acquisition. Fern had built the downstream layer that turns an API definition into something developers can understand and use. Postman already owned a broad upstream workflow for designing, testing, and collaborating on APIs, plus access to more than 500,000 organizations.[3] Combining the two gave Postman a stronger end-to-end API platform and gave Fern a route into an installed base it could not reach as quickly alone.
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Founding Story
Danny Sheridan, Deep Singhvi, and Zach Kirsch started Fern in 2022. Sheridan and Singhvi had met at the University of Michigan in 2015, then spent four years at Amazon and Palantir. There they saw Smithy and Conjure, internal systems that generated bindings in languages such as Python, TypeScript, and Java.[4]
The immediate trigger was failure. In Fern's January 2023 Show HN, the founders wrote, “We built Fern after our previous ed tech startup failed.” They had spent too much time writing repetitive API code instead of building the product.[5] OpenAPI helped describe endpoints, but the generated clients still needed templates, scripts, manual registry publishing, and language-specific repairs.
Fern joined YC's Winter 2023 batch.[6] The early pitch was technical: define an API once, validate it with a compiler, then invoke generators for SDKs, server code, Postman collections, and an OpenAPI specification. It was an infrastructure product before it was a developer-experience brand.
The team spent more than 18 months finding its first customer, Candid Health. Singhvi later said its 300-plus customer Slack channels “light up daily” with feature requests.[1] That slow start revealed a high-trust product shaped through close work with API teams.
Timeline
- 2022: Sheridan, Singhvi, and Kirsch leave Amazon and Palantir to start Fern. Postman CEO Abhinav Asthana invests as an angel.[1]
- January 2023: Fern launches publicly as a compiler and generator system for APIs.[5]
- 2023-24: Candid Health becomes the first customer; Fern adds documentation and wins API-first companies including ElevenLabs.
- April 2025: Bessemer leads a $9 million Series A. Fern reports more than 150 customers.[4]
- January 8, 2026: Postman acquires Fern. The full team joins; the product and brand continue.[2]
- May 2026: Fern relaunches its site around agent experience, self-hosting, SSO, RBAC, and localization.[7]
What They Built
Fern accepts OpenAPI, AsyncAPI, Protobuf/gRPC, OpenRPC, or Fern's own definition format. Its compiler validates the input, then generators produce client libraries in TypeScript, Python, Java, Go, Ruby, C#, PHP, Swift, and Rust. Fern can publish those packages and layer custom code over deterministic output.[8]
Fern Docs uses the same source material for API references, code examples, guides, and interactive exploration. Content can live in Git-backed Markdown, while non-engineering teams use a browser editor. Enterprise customers buy authenticated documentation, role-based access, localization, self-hosting, and support.
The combined product removed a common fracture. A company could otherwise use one system for docs, another generator for SDKs, scripts for package publication, and manual work to keep examples aligned. Fern made the API definition the shared input and treated the produced artifacts as one release surface.
Customer evidence illustrates the workload. ElevenLabs says its APIs change several times a day, its SDKs often receive thousands of lines per week, and the generated JavaScript/TypeScript and Python packages receive more than one million combined weekly downloads. Its Fern-hosted docs reach 1.5 million unique users per month.[9] These are vendor-published case-study figures, but they show why deterministic output mattered more than a code-generation demo.
Fern also expanded toward AI consumers through AI search, machine-readable documentation, an MCP server generator, and an agent-first CLI. The founders' 2025 thesis was that agents would evaluate APIs, obtain credentials, write integrations, and adapt to changes with less human work.[4]
Market Position
Target Customers
Fern targeted developer-experience and API-platform teams with public or partner APIs. Early customers included Candid Health, Square, Webflow, ElevenLabs, LaunchDarkly, and Intercom. By acquisition, the public list included Auth0, Adobe, and Twilio.[2]
The economic buyer was an engineering or developer-platform leader who could compare the subscription with a dedicated SDK or documentation team. The daily users included engineers, technical writers, developer advocates, support staff, and outside developers consuming the output.
Market Size
No defensible standalone market-size estimate appeared in the evidence. The more useful signals are workload and distribution. Fern crossed 200 customers and millions in annual revenue; Postman said its platform served more than 500,000 organizations, including 98% of the Fortune 500.[1][3] The gap between those figures explains the acquisition opportunity better than a generic API-economy forecast.
Competition
Fern competed with several choices rather than one product. Companies could build internal generators, use OpenAPI Generator, buy SDK generation from Stainless or Speakeasy, publish docs through Mintlify or ReadMe, run Docusaurus, or maintain everything by hand. Fern's customer corpus repeatedly presents the combined docs-and-SDK workflow as the reason customers consolidated tools.[10]
Its position depended on output quality and service. The founders argued that common generators mishandled language idioms and production features such as OAuth flows and streaming.[4] Dedicated Slack channels and white-glove migrations helped Fern close the gap between a general compiler and each customer's real API.
Business Model
Fern used an open-core SaaS model. The CLI and generators were open source, making the product inspectable and giving developers a low-friction path to try it. Hosted docs, team workflow, publishing, enterprise controls, self-hosting, and support created paid tiers.
The current pricing page lists a free Hobby plan, a Team plan at $150 per month when billed yearly, and custom Enterprise contracts.[11] That public floor is not a reliable proxy for average contract value. Fern's hands-on migrations, security features, and customer Slack channels point to larger enterprise relationships.
Fern also spent heavily on trust signals. Its early-2025 marketing redesign cost roughly $100,000 over three months and incorporated more than 50 pieces of feedback.[12] For developer infrastructure, the website was evidence of the polish customers could expect from their own generated docs. The investment made the two-product story visible before the Series A and acquisition.
Traction
Fern grew from its first customer after 18 months to more than 150 customers by April 2025 and more than 200 by January 2026.[4][2] Sheridan described millions in annual revenue and a 25-person team. The open-source repository later reached about 3,700 stars and 332 forks.[1][8]
Bessemer led the $9 million Series A in April 2025, then publicly celebrated the Postman transaction as an acquisition of a portfolio company.[13] No observed source disclosed total funding, valuation, acquisition price, founder liquidity, or investor returns.
Post-Mortem
Event: Postman bought the downstream API layer
Postman announced the acquisition on January 8, 2026. The full Fern team joined, while the product, brand, and roadmap remained intact.[3] Postman CEO Abhinav Asthana said, “Great APIs are defined by great developer experiences,” and linked documentation and SDKs directly to API adoption.[14]
Mechanism: the output completed Postman's workflow
Postman helped teams design, test, and collaborate on APIs. Fern handled what happened after an API was ready to expose: documentation, client libraries, package distribution, and integration experience. The products met at the API specification. Fern could extend Postman's workflow without asking users to rebuild the underlying API.
The commercial fit was equally direct. Fern had strong product proof across more than 200 customers, but Postman had hundreds of thousands of organizational accounts. Fern's high-touch sales and implementation model had produced quality and retention signals. Postman could supply reach.
Alternative explanation: talent or feature acquisition
A 25-person startup selling adjacent developer tooling could have been a talent acquisition or a feature folded into Postman. The observed integration argues against that narrow reading. Both companies said Fern would keep its product and brand. Postman added Fern to its product navigation, and Fern continued shipping, hiring, publishing customer cases, and relaunching its marketing around agents after the transaction.
Outcome: independent identity, platform economics
Fern did not fail as a standalone business. It found customers, raised a Series A, and generated millions in annual revenue. The acquisition reflects platform economics: once API design, testing, documentation, SDKs, and agent access converge around the same source descriptions, the larger platform can distribute the specialized product more efficiently.
The price and returns remain unknown. The definitive facts are narrower: buyer and seller called it an acquisition, Bessemer recognized the exit, the team transferred, and Fern continued inside Postman.
Key Lessons
- Internal tools can become external markets. Smithy and Conjure proved that excellent SDK generation was worth dedicated teams. Fern sold that capability to companies without Amazon's budget.
- Eighteen months can still be early. The first customer took time, but Candid Health exposed a recurring enterprise problem and became the reference for a product shaped through close support.
- One source beat two products. Docs and SDKs looked like separate categories. Their shared dependency on the API definition made the combined workflow more valuable.
- Craft was part of the sale. Fern sold developer experience, so its generated code, customer support, and own website all had to demonstrate care.
- Distribution completed the exit. Fern brought the downstream product; Postman brought the installed base. The same API specification connected their roadmaps.
Sources
- Danny Sheridan: acquisition announcement and company metrics
- Fern: joining Postman
- Postman: acquisition announcement
- Bessemer: founder interview and $9 million Series A
- Hacker News: Fern's January 2023 launch
- Y Combinator: Fern company profile
- Fern: 2026 agent-experience positioning
- GitHub: fern-api/fern
- Fern: ElevenLabs customer case
- Fern: customer and competitor corpus
- Fern: pricing
- Fern: 2025 marketing-site build
- Bessemer: portfolio acquisition statement
- Business Wire: Postman acquisition release
- Model Context Protocol: November 2024 specification
- OpenAPI Initiative: May 2024 Arazzo release