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MerciApp: our review

MerciApp corrects and rephrases French text from a French publisher, with direct integration into Gmail, Zendesk, Slack or Intercom. Correction goes through an unnamed third-party language provider, which changes the picture for confidential text.

Data in the EUFree version, then paid·from €144/yearFrench
Go to MerciApp's website (opens in a new tab)

What we take away from it

What counts in its favor

  • French publisher (J2S3, Courbevoie): MerciApp's servers are hosted in France with Amazon Web Services, according to its privacy policy.
  • A real, permanent free tier exists, with no credit card: 600 words analyzed and 3 Transform rephrasings a day, useful for testing before equipping a team.
  • Direct integration into tools already in use (Gmail, Zendesk, Slack, Intercom) avoids making a support or sales team switch screens to correct a message.

What counts against it

  • Correction isn't handled in-house: the terms of use state that texts are shared with a "recognized language solutions publisher," unnamed, which keeps them for 15 days for that purpose.
  • That same provider then keeps the anonymized texts "for debugging and improving the service": the promise shown on the homepage ("your texts are never reused to train AI") is more categorical than what the terms of use detail.
  • The optional LLM-based feature goes through Microsoft as a subprocessor, even though the data stays hosted in France: a firm must accept this knowingly before turning it on.

Solid for everyday French correction hosted in Europe, provided you leave the optional AI feature aside and check with MerciApp who that unnamed language provider is before sending it a confidential document.

The facts

First paid tier
€144/year — Assist, entry tier, per user, billed annually
Data hosting
Data in the EU · source
Data verified on
30 July 2026

What happens to your data

Is your data used to train their models?
Not verified
Subprocessors
The terms of use cite a "recognized language solutions publisher," unidentified, which processes texts for correction and keeps them for 15 days before deleting identifying data; the anonymized data is then kept for debugging and improving the service. For the optional LLM-based AI feature, MerciApp states it uses Microsoft, which hosts this data in France.
Retention
Text is analyzed by the correction engines "then deleted," according to the privacy policy. The language provider keeps the text for 15 days for correction purposes before deleting identifying data.

MerciApp in detail

MerciApp corrects, rephrases and applies internal style rules directly inside the tools a team already writes in: messaging, customer support, instant messaging. The publisher, the French company J2S3 based in Courbevoie, positions it as a proofreader designed for the team rather than for individual writing.

What it actually does

Three building blocks make up the product. Correct flags and fixes spelling, grammar and typography mistakes in real time while typing. Transform rephrases a message to match the brand's tone, directly inside Gmail, Zendesk, Slack or Intercom: a support team can thus keep a consistent tone without going back to a fixed template. Expand inserts predefined text snippets via a keyboard shortcut, for replies that come up often. Everything is managed from an admin interface that tracks usage per user, useful for a manager who has to justify a proofreading budget. The publisher claims a corpus of over 250 million words and more than 10,000 syntax rules built up over thirty years of natural language processing, an argument it plays up against generic proofreaders.

Why it interests us in particular

MerciApp spells out in black and white one of the two points we check systematically in this comparison: hosting. Its privacy policy states that the servers are in France, at Amazon Web Services. For an SME subject to GDPR without a dedicated legal department, having this information written in black and white saves having to ask for it by email — a criterion we check on every proofreader in this comparison. We happily recommend it in our automation engagements for support teams that write all day in a third-party tool and don't have time to reread every message.

Where it falls short

The second point, model training, is hazier. The homepage promises that texts "are never reused to train the AI". The terms of service, however, specify that correction goes through a "recognised provider of language solutions" not publicly identified, which keeps the text for 15 days, then keeps the anonymised version for debugging and service improvement. That doesn't contradict the homepage's promise, but it isn't the same guarantee either, and a firm that wants to know exactly who reads its texts has no answer on this point. The optional AI feature, meanwhile, adds Microsoft as a subprocessor: hosted in France according to the terms of use, but one more company name to get validated by whoever handles compliance.

Our recommendation

For a team writing in French in messaging or support tools, MerciApp ticks the European hosting box better than most of its competitors. Before running a confidential document through it, better to ask MerciApp for the name of the language provider and leave the optional AI feature switched off until that point is clarified.

Who it's for, and who it isn't

Suited for

  • Support or sales teams writing in third-party tools (Gmail, Zendesk, Slack, Intercom) who want correction integrated directly
  • French SMEs that want documented hosting in France for basic correction, without turning on the optional AI features
  • Organizations that want to test before paying: the permanent free tier is enough to assess correction quality on real use

Not a fit

  • Firms handling strictly confidential documents that want to know exactly who reads the text: the third-party language provider isn't publicly named
  • Organizations that refuse any American subprocessor for their data, even hosted in France: the optional AI feature goes through Microsoft
  • Teams that need a public, detailed GDPR DPA: the mentions consulted point to the terms of service, with no dedicated document online

Frequently asked questions

Does my text leave my infrastructure with MerciApp?
Yes, systematically: correction goes through MerciApp's servers, hosted in France with Amazon Web Services, then through an unnamed third-party language provider that processes the text for 15 days. It's not a tool that stays on the device, unlike locally installed software.
Does MerciApp use my texts to train an AI?
The homepage rules it out categorically. The terms of use are more nuanced: the language provider keeps the anonymized texts for "debugging and improving the service" after correction. That's not the same guarantee, and neither document specifies how long this anonymized data is kept.
How much does MerciApp cost for a team?
The Assist tier starts at €12/month per user billed yearly (€144/year), or €24/month billed monthly. A permanent free tier exists (600 words analyzed and 3 rephrasings a day). The Enterprise offering, with SSO and centralized management, is quote-based.
Should I be wary of MerciApp's AI feature?
It's optional and separate from basic correction: it relies on language models run via Microsoft, hosted in France according to the terms of use. For a confidential document, better to turn it off until you've confirmed exactly what the contract covers for your organization.
What's the difference with Antidote?
Antidote processes its core correction locally on the device; MerciApp is designed first for a team writing in online tools (messaging, customer support) and systematically sends the text to its servers. The choice depends on the use case: individual writing on a fixed workstation for Antidote, correction built into team tools for MerciApp.

Alternatives to MerciApp

Our sources

Prices and hosting terms change often. We recheck them periodically, but the publisher's page remains the only up-to-date reference.

Is MerciApp the right choice for you?

We measure this tool against your real constraints — budget, privacy, your team's skill level — before you sign an annual subscription.

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