Theory of operation
The SDK does the hard part on-device, in microseconds, with zero heap. The cloud does the thinking. You wake up to an answer, not a stack trace.
Catch
The fault hook fires before reset. PC, SP, EXCCAUSE on ESP32 — CFSR, HFSR, MMFAR, BFAR on Cortex-M — plus the running task name.
capture ≈ 14 µsSurvive
The dump is parked in RTC NOINIT (ESP32) or Backup SRAM (STM32). It outlives the reboot and ships on next boot — HTTPS, or UART for air-gapped boards.
601 B persistedResolve
Your ELF, uploaded once, turns a raw program counter into function · file · line via the DWARF debug tables. No symbols on the device.
0x400D2A4C → sensor.c:87Diagnose
Claude reads the registers, breadcrumbs, and resolved frame together — then writes the root cause and a fix prompt you paste into Cursor or Copilot.
root cause ≈ 41 sFunctional description
Everything from the crash register to the pull request. Built by a firmware engineer who got tired of crash reports that say "Guru Meditation Error" and nothing else.
AI root cause, not just a stack trace
Other tools hand you registers and frames — you still do the diagnosis at 9 AM with cold coffee. Firmware Sentry hands you the sentence, plus a ready-made prompt for your IDE's AI.
Root cause: i2c_handle is NULL — sensor_read() runs before
i2c_init() completes after brown-out, at sensor.c:87.
Fix: guard the handle and move i2c_init() ahead of task start.
Survives reset
RTC NOINIT on ESP32, Backup SRAM on STM32. The dump is written before the watchdog bites, and uploads on the next boot.
DWARF symbols
Upload the ELF once per build. Every PC address resolves to function, file, and line automatically — verified against esp_app_get_elf_sha256().
Breadcrumbs
A 10-event ring buffer survives the crash. See exactly what the device did in the seconds before the fault — state changes, retries, sensor reads.
No WiFi? No problem.
Air-gapped board? Pipe crash data over UART through gateway.py to the cloud. Works on any non-networked MCU.
Email the instant it breaks
Fault signature, task name, and a direct link to the AI diagnosis — in your inbox before the device finishes rebooting.
Pure C99, audit it yourself
~4 KB flash, zero heap allocations, no RTOS lock-in. Apache-2.0 on GitHub — read every line before it ships in your product.
SDK characteristics
You'd check the table before choosing a voltage regulator. Check it before choosing a crash reporter.
| Parameter | Conditions | Min | Typ | Max | Unit |
|---|---|---|---|---|---|
| Flash footprint | core + HTTPS transport | — | 4.1 | 6.0 | KB |
| Persistent crash dump | RTC NOINIT / Backup SRAM | — | 601 | 601 | B |
| Heap allocations | entire SDK lifetime | 0 | 0 | 0 | allocs |
| Fault capture time | registers + task + breadcrumbs | — | 14 | 50 | µs |
| Breadcrumb buffer | ring, survives reset | — | 10 | 10 | events |
| Time to AI diagnosis | device reboot → dashboard | — | 41 | 90 | s |
| Integration time | init + provision + one breadcrumb | — | 30 | — | min |
Memfault is great. It's also $3,495/mo and a sales call.
An honest comparison. We built Firmware Sentry for the team that wants answers today, not a procurement cycle.
Memfault
- Growth plan starts at $3,495/mo, quote required
- AI covers fleet-wide release trends, not individual crashes
- 30-day debugging retention on Growth tier
- Full OTA + fleet management platform — more than most small teams need
- Free tier limited to Nordic nRF chips via nRF Cloud
Firmware Sentry
- Free tier, paid from $59/mo, fully self-serve
- AI writes a root cause + IDE fix prompt for every individual crash
- 1-year retention on Growth tier
- Focused on crash diagnosis — nothing to configure that you don't need
- Free tier works on any supported chip, no card
Ordering information
Pay for crashes analyzed, not seats. Start free on your bench, upgrade when you ship, cancel anytime.
Free
Prove it on your own hardware first. No card.
- 50 diagnoses/mo
- 10 devices
- 7-day retention
- DWARF resolution
Starter
Small teams shipping to real customers.
- 500 diagnoses/mo
- 10 devices
- 90-day retention
- Email alerts
- REST API
Growth
Scaling fleets and contract firmware shops.
- 2,000 diagnoses/mo
- 100 devices
- 1-year retention
- Bulk device API
- Priority support
Scale
Industrial & medical device fleets.
- 10,000 diagnoses/mo
- 1,000 devices
- Unlimited retention
- SSO / audit logs
- Dedicated support