Startups > Tessl

Tessl

Tessl enables teams to develop and maintain code through specifications instead of traditional coding.

Series A $125M total Founded 2024 London, England 25 employees

Tessl is an AI-native software development platform that uses Spec-Driven Development to enable teams to write, test, and maintain code through natural language specifications. It prevents AI hallucinations and API errors by maintaining a registry of 10,000+ verified library specs, allowing developers to specify intent once and have the platform automatically maintain code alignment. Unlike traditional AI coding assistants that bolt automation onto existing workflows, Tessl reimagines development as spec-centric rather than code-centric.

Problem solved

AI coding assistants hallucinate APIs, fail silently, and require constant manual oversight, slowing development and introducing bugs into production systems.

Target customer

Software development teams and engineering organizations building AI-native applications, from early-stage startups to enterprise development departments

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Founders

Guy Podjarny

Founder & CEO

Former CTO of Akamai and founder of Snyk (scaled to $8B), Israeli-born engineer with Israeli Army cybersecurity background and 100+ angel investments.

Funding history

Seed $25M April 2024 Led by boldstart, GV

Series A $100M November 2024 Led by Index Ventures · Accel Partners, GV, boldstart

Total raised: $125M

Industries

Artificial Intelligence (AI) Software Engineering Software

Pricing

Not publicly available. Spec Registry is free in open beta; Tessl Framework available by request in closed beta. Product launched September 2025 with pricing details undisclosed.

Integrations

Java, JavaScript, Python (with more languages planned); Snyk (security scoring); partnerships with other AI coding assistant platforms planned

Tech stack

GSAP (JavaScript frameworks) jQuery (JavaScript libraries) Open Graph HTTP/3 PostHog (Analytics) HSTS (Security) Google Font API (Font scripts) Google Workspace (Email) Google Hosted Libraries (CDN) cdnjs (CDN) Cloudflare (CDN) Webflow (Page builders)

Website

tessl.io/

Competitors

GitHub Copilot

Line-of-code completion tool that bolts AI onto existing workflows rather than reimagining development as spec-driven.

Cognition Devin

Creates entire programs from prompts but lacks specification control and maintenance layer for ongoing code alignment.

Codeium

AI-assisted development tool focused on automating existing workflows rather than defining new AI-native development paradigm.

Replit

Cloud IDE with AI features but not focused on specification-driven development or automated code maintenance.

Tabnine

Code completion and generation tool without specification-driven architecture or registry of verified library APIs.

Why this matters: Tessl is backed by legendary founder Guy Podjarny (Snyk's $8B exit) and has raised $125M in 9 months, validating early demand for a fundamentally different approach to AI-native development. The specification-driven paradigm directly addresses real failures of current AI coding tools—hallucinations, silent failures, and lack of maintainability—positioning it as a potential category-defining platform.

Best for: Development teams building AI-native applications who want reliable, maintainable code with minimal hallucinations and automatic ongoing maintenance.

Use cases

Specification-Driven Development

Teams write natural language or code specifications defining requirements once, then Tessl generates and maintains code to match those specs. If requirements change, developers update the spec and Tessl automatically updates the implementation, reducing the manual code maintenance burden.

API Reliability and Version Management

The Spec Registry prevents AI from hallucinating library APIs by providing verified specifications for 10,000+ external libraries. When libraries update versions, specifications can be updated centrally and Tessl automatically maintains code compatibility without developers manually hunting for deprecated API calls.

Testing and Validation in Sandbox

Teams can test AI-generated code in a sandbox environment, flag issues, and iterate on specifications without deploying untested code. This catch-and-fix loop ensures AI-generated code meets quality standards before reaching production.

Alternatives

GitHub Copilot Choose if you want seamless integration with existing developer workflows and broader language support, but accept less structured code quality control.

Cognition Devin Choose if you need an autonomous agent for end-to-end project creation from natural language, but without specification-driven maintenance and API verification.

Traditional AI Coding Assistants (Codeium, Tabnine) Choose if you need lightweight code completion without the overhead of specification management, but accept higher hallucination rates and manual maintenance.

FAQ

What does Tessl do? +

Tessl is an AI-native software development platform where developers write specifications in natural language or code, then Tessl generates implementation code. Teams test code in a sandbox, iterate on specs, and Tessl automatically maintains the code to match the specification. It includes a registry of 10,000+ verified library specs to prevent API hallucinations.

How much does Tessl cost? +

Pricing is not publicly available. The Spec Registry is free in open beta. The Tessl Framework is available by request in closed beta. Pricing details will be announced as the product enters full commercial availability.

What are alternatives to Tessl? +

GitHub Copilot (line-of-code completion), Cognition Devin (autonomous program generation), Codeium (AI code completion), Replit (cloud IDE with AI), Tabnine (code generation), and DiffBlue (automated test generation).

Who uses Tessl? +

Target customers are development teams and engineering organizations building AI-native applications. Specific paying customers have not been publicly disclosed as the company is in early access/beta phase.

How does Tessl compare to GitHub Copilot? +

Copilot completes lines of code and bolts AI onto existing workflows. Tessl reimagines development as spec-driven, generating entire functions/modules from specifications with automatic maintenance and API verification to prevent hallucinations. Tessl is more ambitious in redefining the development paradigm rather than automating traditional development.