An Alternative to OpenZeppelin Defender Monitor

Hosted Defender was scheduled to retire on July 1, 2026. If you relied on it for on-chain alerts, here are your options, and where Chainitor does and does not fit.

Facts as of November 2026, with sources linked.

OpenZeppelin and Defender are trademarks of their owner. Chainitor is not affiliated with OpenZeppelin.

What happened to Defender

On June 30, 2025 OpenZeppelin announced it was phasing out Defender, disabled new sign-ups that day, and set July 1, 2026 as the date the platform would retire; its sunset FAQ gives the same date for retiring the hosted service. In its place it published open-source versions of the two core pieces, Relayer and Monitor, which teams run in their own environment, and offers a managed service for teams that want OpenZeppelin to host them. The FAQ describes the open-source tools as close to feature parity and licensed under AGPL v3.

So the question for a team that used Defender Monitor is not whether to move, but where: self-host the open-source Monitor, pay for a managed deployment of it, or use a hosted alerting service.

Option 1: OpenZeppelin Monitor (open source)

OpenZeppelin Monitor is the official successor. It is a Rust service, licensed AGPL-3.0, with releases continuing through 2026 (v1.7.0 in October). According to its README and documentation, it:

  • watches EVM-compatible networks, Stellar and Solana, with partial Midnight support;
  • matches events and transactions with flexible filter expressions defined in configuration files;
  • notifies via Slack, Discord, email (SMTP), Telegram and webhooks, or runs custom Python, JavaScript or Bash scripts.

Where it is stronger than Chainitor: it is free to run, open source, covers non-EVM chains, supports Discord and custom scripts, and its filter expressions are more expressive than a form. The cost: you operate it, which means hosting, RPC endpoints, configuration in files, upgrades and keeping the monitor itself monitored.

Option 2: OpenZeppelin's managed service

For teams that want the open-source tools without running them, OpenZeppelin's announcement mentions customised managed service solutions covering hosting, deployment, monitoring and maintenance, requested through a form. Pricing is not published. It is the natural choice if you also need Relayer and want a single vendor for both.

Option 3: a hosted alerting service such as Chainitor

Chainitor is a hosted, non-custodial alerting service for EVM chains. You create monitors in a web app, with no servers or configuration files, and alerts go to email, Slack, Telegram, PagerDuty or a webhook. Prices are published: Starter is $29 a month and Pro is $49 a month, with a 7-day trial. Here is how common Defender Monitor jobs map onto it:

What you alerted on Chainitor monitor
Alert when a contract emits an event Event monitor
Alert when a function is called on a contract Function call monitor
Alert on failed (reverted) transactions Failed transaction monitor
Alert on transfers above a value Transaction value monitor
Alert when a relayer or keeper wallet runs low on gas Balance monitor
Alert on Safe owner, threshold, guard or module changes Safe security monitors

Function call, failed transaction and transaction value monitors are on the Pro plan. Event, balance and Safe monitors are on every plan.

Where Chainitor is not a fit

  • Relaying and signing. Chainitor never holds keys or sends transactions. Use OpenZeppelin Relayer.
  • Custom code on alert. There is no equivalent of Defender Actions. Send alerts to a webhook and run the logic in your own service.
  • Non-EVM chains, and EVM chains outside its list. Chainitor supports seven EVM networks, plus public testnets where available.
  • Arbitrary filter expressions. Each monitor type has a fixed set of options rather than a general expression language.
  • Discord. Chainitor does not deliver to Discord.

Moving your Defender monitors

  1. List what each Defender monitor watched: contract, chain, events or functions, and where it notified.
  2. Decide per monitor whether it needs expression-level filtering or non-EVM support (OpenZeppelin Monitor) or a standard condition (a hosted service).
  3. Recreate the standard ones as Chainitor monitors and point them at the same Slack, Telegram, PagerDuty or webhook destinations.
  4. Run a test: trigger the event or function on a testnet and confirm the alert arrives.

Frequently asked questions

Is OpenZeppelin Defender still available?

Not for new teams. OpenZeppelin's announcement of June 30, 2025 closed new sign-ups that day, and its Defender sunset FAQ says the hosted service was scheduled to retire on July 1, 2026. It points teams to its open-source Monitor and Relayer, which can be self-hosted or run through an OpenZeppelin managed service.

What is the official replacement for Defender Monitor?

OpenZeppelin Monitor, an open-source service written in Rust and licensed under AGPL-3.0. It watches EVM, Stellar and Solana networks, with partial support for Midnight, and sends notifications to Slack, Discord, email, Telegram, webhooks or custom scripts. You run and operate it yourself, or ask OpenZeppelin about a managed deployment.

Can Chainitor replace Defender Relayer or Actions?

No. Chainitor only observes and notifies: it never holds keys, signs or sends transactions, and does not run custom code. For relaying, OpenZeppelin's open-source Relayer is the direct successor. Chainitor can still trigger your own automation by sending alerts to a webhook.

Which chains does Chainitor support?

Ethereum, Polygon, Arbitrum, Optimism, BNB Chain, Base and Robinhood Chain, plus public testnets where available. Chainitor does not monitor non-EVM chains, so teams on Stellar or Solana should look at OpenZeppelin Monitor.

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