Beacon vs Spanlens

Beacon and Spanlens are both inference engines & infra tracked by AIDiveForge. Below is a side-by-side comparison of pricing, capabilities, platforms, and ownership — sourced from each tool's live website and verified before publishing.

Beacon

Beacon is an open-source endpoint telemetry layer that runs locally alongside AI agents, capturing prompts, tool calls, file modifications, and approval workflows before any of that activity disappears into the void. It normalizes that telemetry and forwards it to SIEM platforms like Wazuh, Elastic, or Splunk, so security teams can apply the same detection logic they already run against the rest of the fleet. The architecture is self-hosted by design — no data leaves the endpoint unless you route it there yourself. The project is early-stage; the plugin ecosystem covers the major local agent harnesses but gaps exist for less common runtimes. Teams with agents not yet on the supported list write custom collector plugins — which means more surface area to maintain.

Spanlens

Spanlens sits in front of your LLM provider via a single baseURL change, recording every call's cost, latency, tokens, and full request-response body with no SDK rewrite required. Agent runs surface as waterfall span trees so you can identify the one step consuming 80% of wall-clock time. The model recommender flags GPT-4o calls that look like classification tasks and shows the cost delta if you swap — with numbers from your own traffic, not benchmarks. The eval and experiment layer lets you replay a fixed dataset across prompt versions before you ship, so quality regressions don't surprise you in production. PII scanning and anomaly detection run at log time, which matters when sensitive data crosses the wire at 3 a.m. with nobody watching.

Attribute	Beacon	Spanlens
Pricing	Free	Paid
Price	—	$29/mo
Free trial	No	No
Open source	Yes	Yes
Has API	No	Yes
Self-hosted option	Yes	Yes
Platforms	Linux, macOS, Windows	Node.js, Python, Next.js, Edge, self-hosted
Pros	Runs entirely on the local endpoint with no external data forwarding required, so organizations in regulated industries can capture AI agent telemetry without breaching data residency requirements. Normalizes agent activity into structured telemetry compatible with Wazuh, Elastic, and Splunk, so security teams can write detection rules against AI agent behavior using the same tooling they already maintain for the rest of the infrastructure. Captures the full activity chain — prompts, tool calls, file edits, approval workflows — which means audit trails hold up when a compliance team asks exactly what an agent touched and when, rather than reconstructing context after the fact. MIT-licensed and free with no paid tier, so there is no licensing negotiation before a regulated-industry proof of concept, and the full source is auditable by the security team before deployment. Structured for MDM-managed deployments, so enterprise IT teams can push Beacon alongside agent runtimes through existing device management pipelines rather than requiring manual per-machine setup.	Proxy-layer instrumentation via a single baseURL change, so existing code requires no structural rewrite and every provider call is captured from day one rather than after a manual instrumentation sprint. Per-user and per-route cost attribution, which means you can identify the specific customer or endpoint burning disproportionate budget before it compounds across a billing cycle. Agent waterfall trace trees with critical-path highlighting, so a slow or expensive step in a multi-agent run is pinpointed in seconds instead of reproduced manually in a staging environment. Experiment runner replays a fixed dataset across prompt versions and models with quality, cost, and latency compared side by side, which means you ship with evidence that v8 is better than v7 rather than finding out the hard way in production. Self-hosted deployment via Docker Compose under MIT license, so teams with data residency or audit requirements can run the full platform without sending trace data to a third-party cloud.
Cons	Plugin coverage is scoped to the major local agent harnesses the project explicitly supports; agents running on runtimes outside that list produce no telemetry until a custom collector plugin is written and maintained — which delays security coverage for any team adopting a newer or less common agent framework. There is no hosted dashboard or managed backend, which means the security team owns the full stack: endpoint deployment, SIEM routing, schema mapping, and alert logic. Teams without an operational SIEM who want a turnkey monitoring UI will abandon Beacon for a hosted observability product before the first sprint ends. The project carries a small contributor base at the time of publication; teams depending on active maintenance for fast-moving agent runtimes accept the risk that plugin support lags runtime updates, requiring internal engineering to bridge the gap or switch to a vendor with a dedicated support contract.	PII detection is regex-based and runs at log time as a flag — not a pre-storage redaction guarantee. Teams operating under HIPAA or SOC 2 controls where sensitive data must never reach a log store, even briefly, need a dedicated redaction layer upstream of Spanlens or a different architecture entirely. The LLM-as-judge eval scoring is a single 0–1 scalar per response. Teams needing structured, multi-criteria evaluation rubrics — for example, factual accuracy scored separately from tone and policy compliance — hit the ceiling of what the built-in scorer expresses and end up maintaining a custom eval harness alongside Spanlens. At high request volumes where the proxy layer adds measurable latency to every call, teams running latency-sensitive production paths at scale have moved to SDK-side instrumentation tools or full APM platforms with LLM plugins, where the observability path is out of band rather than in the critical path.

Bottom line

Beacon is free while Spanlens is paid; only Spanlens exposes a public API. Choose based on which difference matters most for your workflow.

Frequently asked questions

What is the difference between Beacon and Spanlens?

Beacon is Free and open source, while Spanlens is Paid and open source. Compare pricing, free trial, API, platforms, and pros/cons in the table above on AIDiveForge.

Is Beacon better than Spanlens?

It depends on your workflow. Use the side-by-side attributes (pricing, open source, API, self-hosted, platforms) to decide. AIDiveForge does not rank a universal winner — we publish verified facts so you can choose.