VOL. XCIV, NO. 247

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Friday, December 26, 2025

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Tool Comparison

Firefly III vs MesoSim comparison

Compare pricing, supported platforms, categories, and standout capabilities to decide which tool fits your workflow.

Quick takeaways

Firefly III adds Portfolio, Webhooks, and Other coverage that MesoSim skips.

MesoSim includes Backtesting, Options & Derivatives, Data Visualizations, Paper Trading, AI, and AI Chat categories that Firefly III omits.

In depth comparison

Firefly III

firefly-iii.org

An open-source, self-hosted personal finance manager licensed under AGPLv3. Offers full double-entry bookkeeping, REST APIs, and optional event webhooks. Exchange-rate conversion is available from v6.2 onward as an opt-in feature. Bank connections are handled separately through the Firefly Data Importer app.

Platforms

WebAPI

Pricing

Free

Quick highlights

Self-hosted open-source personal finance manager (AGPLv3 license).
Supports double-entry bookkeeping with budgets, categories, tags, and detailed reporting.
Comprehensive REST API (JSON) with OAuth2 and Personal Access Tokens, plus a full OpenAPI specification.
Event webhooks for transaction create/update/delete, enabled through environment configuration.
Separate Data Importer tool supports CSV and CAMT.053, with optional bank integrations via Salt Edge, GoCardless, and SimpleFIN.

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MesoSim

mesosim.io

Options strategy backtesting SaaS with low-code strategy definitions, observability (events log), risk graphs/Greeks, margin reporting, an options valuation model/solver, and an implied-volatility surface viewer. Plan gating: Free includes 25 runs; Standard ($1000/yr) unlocks unlimited SPX + BTCUSD/ETHUSD options backtests plus sharing/exports and 1 MesoLive paper-trading account; Advanced ($1250/yr) adds RUT/VIX/GLD, margin models, vol surface/HD risk graphs, and hourly risk traces (plus up to 2 paper accounts). Live trade execution is a paid MesoLive add-on; API access is FundPro-only.

Platforms

WebAPI

Pricing

FreeSubscription

Quick highlights

Advanced options strategy backtesting service built around a low-code workflow.
Strategy Definition schema supports multi-leg structures plus entry/exit/adjustments and simulator controls (fill model, commissions/slippage, margin, position monitoring).
TradFi instruments documented for simulation: SPX (data from 2010), RUT/VIX (data from 2012), and GLD (data from 2012), with index vs equity option modeling notes.
Published data availability + vendors and resolution (5-minute): SPX/RUT/VIX/GLD sourced from Cboe Global Markets; BTCUSD/ETHUSD (and historical SOLUSD) sourced from Deribit.
Position Monitor provides 2D/3D risk graphs, PnL, and Greeks, with trace collection intervals (Off/Daily/Hourly).

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Where they differ

Firefly III

Distinct strengths include:

Portfolio Webhooks Other

Self-hosted open-source personal finance manager (AGPLv3 license).
Supports double-entry bookkeeping with budgets, categories, tags, and detailed reporting.
Comprehensive REST API (JSON) with OAuth2 and Personal Access Tokens, plus a full OpenAPI specification.
Event webhooks for transaction create/update/delete, enabled through environment configuration.

MesoSim

Distinct strengths include:

Backtesting Options & Derivatives Data Visualizations Paper Trading AI AI Chat

Advanced options strategy backtesting service built around a low-code workflow.
Strategy Definition schema supports multi-leg structures plus entry/exit/adjustments and simulator controls (fill model, commissions/slippage, margin, position monitoring).
TradFi instruments documented for simulation: SPX (data from 2010), RUT/VIX (data from 2012), and GLD (data from 2012), with index vs equity option modeling notes.
Published data availability + vendors and resolution (5-minute): SPX/RUT/VIX/GLD sourced from Cboe Global Markets; BTCUSD/ETHUSD (and historical SOLUSD) sourced from Deribit.

Feature-by-feature breakdown

Attribute	Firefly III	MesoSim
Categories Which research workflows each platform targets	Shared: APIs & SDKs Unique: Portfolio, Webhooks, Other	Shared: APIs & SDKs Unique: Backtesting, Options & Derivatives, Data Visualizations, Paper Trading, AI, AI Chat
Asset types Supported asset classes and universes	Other	Options, Cryptos
Experience levels Who each product is built for	Beginner, Intermediate, Advanced	Intermediate, Advanced
Platforms Where you can access the product	Web, API	Web, API
Pricing High-level pricing models	Free	Free, Subscription
Key features Core capabilities called out by each vendor	Unique Self-hosted open-source personal finance manager (AGPLv3 license). Supports double-entry bookkeeping with budgets, categories, tags, and detailed reporting. Comprehensive REST API (JSON) with OAuth2 and Personal Access Tokens, plus a full OpenAPI specification. Event webhooks for transaction create/update/delete, enabled through environment configuration. Separate Data Importer tool supports CSV and CAMT.053, with optional bank integrations via Salt Edge, GoCardless, and SimpleFIN. CSV export available for accounts, budgets, categories, tags, recurring transactions, subscriptions, piggy banks, rules, and more.	Unique Advanced options strategy backtesting service built around a low-code workflow. Strategy Definition schema supports multi-leg structures plus entry/exit/adjustments and simulator controls (fill model, commissions/slippage, margin, position monitoring). TradFi instruments documented for simulation: SPX (data from 2010), RUT/VIX (data from 2012), and GLD (data from 2012), with index vs equity option modeling notes. Published data availability + vendors and resolution (5-minute): SPX/RUT/VIX/GLD sourced from Cboe Global Markets; BTCUSD/ETHUSD (and historical SOLUSD) sourced from Deribit. Position Monitor provides 2D/3D risk graphs, PnL, and Greeks, with trace collection intervals (Off/Daily/Hourly). Volatility Surface viewer to explore implied-vol surfaces with overlays (e.g., open interest, volume, bid-ask spread, Greeks) and playback at 5-minute resolution (non-crypto in current version).
Tested Verified by hands-on testing inside Find My Moat	Not yet	Not yet
Editor pick Featured inside curated shortlists	Standard listing	Standard listing

Frequently Asked Questions

Which workflows do Firefly III and MesoSim both support?

Both platforms cover APIs & SDKs workflows, so you can research those use cases in either tool before digging into the feature differences below.

Do Firefly III and MesoSim require subscriptions?

Both Firefly III and MesoSim keep freemium access with optional paid upgrades, so you can trial each platform before committing.

How can you access Firefly III and MesoSim?

Both Firefly III and MesoSim prioritize web or desktop access. Investors wanting a mobile-first workflow may need to rely on responsive web views.

What unique strengths set the two platforms apart?

Firefly III differentiates itself with Self-hosted open-source personal finance manager (AGPLv3 license)., Supports double-entry bookkeeping with budgets, categories, tags, and detailed reporting., and Comprehensive REST API (JSON) with OAuth2 and Personal Access Tokens, plus a full OpenAPI specification., whereas MesoSim stands out for Advanced options strategy backtesting service built around a low-code workflow., Strategy Definition schema supports multi-leg structures plus entry/exit/adjustments and simulator controls (fill model, commissions/slippage, margin, position monitoring)., and TradFi instruments documented for simulation: SPX (data from 2010), RUT/VIX (data from 2012), and GLD (data from 2012), with index vs equity option modeling notes..

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