PreFlight vs Spanlens

PreFlight 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.

PreFlight

PreFlight installs via npm and runs as a pre-commit gate, scanning AI-generated code for security vulnerabilities in auth flows, database logic, and SQL patterns — then offering deterministic or AI-assisted patches inline. It integrates with VS Code, Cursor, and MCP clients, so the scan happens in the environment where the AI code was written. The free tier caps patches at ten, which is sufficient for evaluation but stops short of daily use on an active codebase. Teams that exceed that ceiling without a pro key lose the fix-application step and are left with scan output only. The repo is open-source and self-hosted, so the scan never phones home.

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	PreFlight	Spanlens
Pricing	Paid	Paid
Price	$19/mo	$29/mo
Free trial	No	No
Open source	Yes	Yes
Has API	No	Yes
Self-hosted option	Yes	Yes
Platforms	CLI, npm, VS Code, Cursor	Node.js, Python, Next.js, Edge, self-hosted
Pros	Runs entirely locally with no cloud dependency for scanning, so code never leaves the machine during the security check — which matters for teams under data-residency or compliance constraints. Pre-commit integration means vulnerabilities surface before they enter the repository rather than at PR review, so the team avoids the back-and-forth of post-commit security findings. RLS and SQL safety checks are explicitly scoped, so the specific class of vulnerability that AI tools most often miss in database logic gets dedicated coverage rather than a generic lint pass. MCP client support lets other tools and editor workflows invoke the scanner directly, so the security gate can be embedded in automated flows without requiring a separate manual step. Open-source codebase allows teams to audit the scan rules themselves, so trust in the tool does not depend solely on vendor claims about what it detects.	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	The free tier caps patch application at ten — once that limit is hit, the tool continues to surface findings but stops applying fixes. A team using AI coding tools daily will exhaust this on a single feature branch, forcing a licensing decision before they have enough production signal to evaluate the tool's accuracy. The scanner is scoped to auth, database, and SQL vulnerability classes. Teams that need coverage across a broader attack surface — dependency vulnerabilities, secret detection, SSRF, or injection beyond SQL — will need a separate tool running in parallel, which means maintaining two scan configurations and reconciling their output. The project shows a single star and no forks on GitHub at the time of curation, with an open issue logged. Teams evaluating this against established SAST tools with large community rule sets and documented false-positive rates will find precious little external evidence of production use — which is the condition under which a security-conscious team switches to a competitor with a longer track record.	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

Only Spanlens exposes a public API. Choose based on which difference matters most for your workflow.

Frequently asked questions

What is the difference between PreFlight and Spanlens?

PreFlight is Paid 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 PreFlight 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.