The verification layer for the AI age
Build verified into everything you ship
Chainletter gives builders a simple API to stamp any file to the blockchain — creating verified, tamper-proof records that any agent or human can check. Add verification to your app, your platform, or your workflow in hours. We built five tools on it ourselves. What will you build?
const res = await fetch(“https://service-link.clstamp.com/webhook/YOUR_API_KEY”, {
method: “POST”,
headers: {
“secret-key”: “YOUR_SECRET_KEY”,
“group-id”: “verified-records”,
“stamp-immediately”: “true”
},
body: formData // FormData with ‘file’ field
});
Built with Chainletter
Five tools. One API. All built in hours.
Every one of these was built on the Chainletter API — most in a single sitting. They’re proof that verification infrastructure doesn’t take months to ship. What will you build?
Credential Platform
A turnkey stamping portal where organizations upload files, stamp them to the blockchain, and distribute verified credentials to recipients — no code required.
CredCLI
A CLI tool that AI agents use to issue blockchain-stamped credentials from the terminal. CSV in, verified PDFs out. Designed to be orchestrated by Claude Code.
DSoul
A decentralized AI skills marketplace. Chainletter verifies creator identities and freezes published skills on IPFS — creating a tamper-proof supply chain for AI capabilities.
Asset Tracker
Timestamped, verified files that follow the custody chain of luxury goods and collectibles. Every ownership transfer is blockchain-stamped, creating an auditable provenance trail.
Credentials Quiz
A vibecoded quiz that issues a real blockchain-stamped credential to anyone who passes. Built in hours as a proof of concept — and it works in production today.
The problem
Builders need verification infrastructure — and it doesn’t exist
Every app, platform, and agent that handles important files needs a way to prove those files are authentic. But building that trust layer from scratch is hard, expensive, and slow.
Your app receives a credential, contract, or skill file — but there’s no standard way to confirm who created it or whether the claimed identity is real
Documents and artifacts on traditional servers can be silently modified after creation — and neither your users nor their agents would know
Blockchain, cryptographic hashing, IPFS, timestamping — the components exist, but integrating them into a production system is a massive engineering lift
How Chainletter solves it
One API. Three guarantees. Any file.
Chainletter gives builders a verification layer they can integrate in hours — not months. Every stamped file carries three provable guarantees.
Prove who created it
Every stamped file is linked to a verified issuer on the blockchain. Your app — or any agent — can confirm the creator’s identity programmatically, with no human in the loop.
Prove it hasn’t changed
A cryptographic hash is recorded on-chain at the moment of stamping. If a single byte is modified afterward, the hash won’t match — instantly exposing the tampering.
Prove when it existed
The blockchain timestamp creates an irrefutable record of when a file was stamped. Agents and users can verify that a record existed in a specific form at a specific time.
Why blockchain
The only verification layer that can’t be gamed
Databases can be hacked. Servers can be compromised. The blockchain can’t be altered — which is why builders trust it as infrastructure.
No one can alter the record
Once stamped, a record cannot be changed, backdated, or deleted — by anyone, including Chainletter. Any system that checks the hash gets a mathematically certain answer.
No single point of failure
Verification doesn’t depend on Chainletter’s servers being online. Your app verifies against the public blockchain — an infrastructure that no single entity controls.
Outlasts every company
Companies close. Servers go offline. Blockchain records persist. A file stamped today is verifiable a decade from now by any system that checks.
For builders
An API designed for machines — that humans love too
One endpoint, header-based routing, real-time events. Every surface is optimized for agents, LLMs, and developers who move fast.
Upload & stamp
Upload a file and stamp it to the blockchain in one call. Chainletter handles IPFS pinning, hash computation, and on-chain indexing. Your app just sends a POST.
List & verify
List groups, check file status, or verify any hash against the blockchain. Three workflows through one GET endpoint — perfect for agents that need to check before they act.
Real-time events
Open an SSE connection and receive events the moment they happen — file uploads, stamp confirmations, failures. Build reactive systems without polling.
LLMs and coding assistants read the docs and generate working integrations — no manual onboarding needed
API key in the path, secret key in the header. That’s the entire auth model — simple enough for any agent to handle
Upload files over time, then stamp them all on-chain in a single PATCH request — built for high-volume workflows
Agent-native tooling
CredCLI — blockchain credentials from the command line
We didn’t just build an API and hope agents would figure it out. We built the tool agents actually use.
CredCLI turns HTML templates and a CSV spreadsheet into signed PDFs, verifiable badges, and blockchain-stamped credentials — in seconds, from the terminal. It ships with a dedicated Agent Guide, auto-generated skill files for Claude Code, and five built-in templates. Tell an agent “Issue diplomas to everyone in recipients.csv” and it handles template selection, rendering, blockchain stamping, and email generation. End to end. No custom code.
Why Chainletter
Verification infrastructure that gets out of your way
No blockchain expertise. No crypto wallets. No months-long build. Just the trust layer your app needs.
The quiz, the asset tracker, and CredCLI were all built in single sittings. Your integration can be too
No wallets, no tokens, no blockchain knowledge — just REST calls and verified records
Compatible with any language, framework, agent runtime, or existing application
Cryptographic hashes create proof that no AI model can forge, replicate, or reverse-engineer
Records are verified against the public blockchain, not our servers. Your trust layer survives no matter what
The same verification works whether the consumer is a person checking a diploma or an agent composing a workflow
Backed by Qubic Labs — Proud recipient of a 2025 development grant from blockchain accelerator Qubic Labs.
Start building
What will you build on Chainletter?
Five tools were built on this API in hours. The verification layer is ready. Your idea is next.
