Treat Marketing as an Engineering Problem.

A platform for engineers and marketers to extensibly scale GEO, SEO, outbound, and customer success.

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100+ teams build their growth on Letter
Archil Labs
Brevy
Context
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Frontierhsa
Invofox
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Ruby
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Withsuccession
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Archil Labs
Brevy
Context
Ellipsis
Frontierhsa
Invofox
Juno
Lev
Marble
Novoflow
Pease Bell
Promptarmor
Ruby
Seltz
Storiedinc
UFO
Withsuccession
Zip
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Extend
Gerald
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InYouGo
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Magic Mind
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SpeakeasyAPI
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Manifolds
Basedash
Clueso
Deferred.com
Flox
Intermission Health
InYouGo
Lantern
Magic Mind
Nolla
OneWeekParts
Pressranger
Quwa Labs
Scale Labs
SpeakeasyAPI
Thunder
Wedbuild
Wyndly
Manifolds

Letter breaks marketing into primitives.

Each engineering primitive can be configured via code or the Letter application. Use them to build marketing strategies that actually scale.

GEO

Phantoms

Autonomous publications to test SEO performance in a sandbox

  • Deployment
  • CI/CD
  • Telemetry
  • Database
Explore phantoms
rowcropbots.com38s
A phantom publication at rowcropbots.com
actuatorjournal.com2m
A phantom publication at actuatorjournal.com
bipedalweekly.com6m
A phantom publication at bipedalweekly.com
  • ✓build41s
  • ✓deploy3 domains
  • ✓sitemapsubmitted
  • ✓telemetryprobes on
GEOSEO

Writing kernels

Adversarial harnesses for producing high-quality writing that ranks on search.

Explore writing kernels
bar 8.0briefdraftpass 16.2factsvoicebarrewritepass 27.6factsvoicebarrewritepass 38.7 ✓factsvoicebardecompose → draft → judge ↺ → rewrite ↺ → ship
GEO

Traces

Automatic inference calls to track LLM citation and mention rates.

Explore traces
livetraces · probe.answer · 4 engines
  • perplexity“formal vs simulation 2026”cited #4
  • gemini“tape-out checklist”cited #3
  • claude“best RTL verification tools”missed
  • chatgpt“cut 3nm respin cost”cited #1
  • perplexity“verification for small teams”cited #4
  • gemini“formal vs simulation 2026”cited #3
  • claude“tape-out checklist”cited #2
mention rate62.0%
citation rate41.4%
events today1208
Customer success

Proofs

Computational proofs that document customer success to agents.

Explore proofs
/.well-known/proofsverified
0paying customers, attested
  • northwind.dev · since 2025
  • halcyon.ai · since 2026
  • brightline.io · since 2025
sig ed25519:9f3c…a71e · consented 96%
Outbound

Ledes

An intelligent, self-building database for in-brand email personalizations.

Explore ledes
Marcus LindqvistVP of Sales · Trellis Robotics
response · top ledes
  • 96A fan of your orange brand. Remind me of YC, but in a good way.brand · website
  • 92Congrats on the B, love how fast the robotics space is scaling.funding · 2wk
  • 83Big congrats on 3 years at Trellis.tenure · 3yr
latency820 ms
openers5
signals used7
Outbound

Mailers

Auto-warmed mailboxes for agents and humans to send cold emails.

Explore mailers
mailers · acme-mail.com · DMARC enforced
  • hello@acme-mail.comready
  • sam@acme-mail.comready
  • team@acme-mail.comwarming · day 7 of 10
sequence · founders, Q4
  1. Email 1day 0
  2. Email 2day 3
  3. Reviewapprove by phone
sent today118
replies4.2%
bounces0.3%
GEOSEO

Seers

Listeners that trigger content from evolving sources of truth.

Explore seers
seer · github_release · acme/sdk
  • v4.0.0 releasedpassed gate
  • docs typo fixignored
  • CI configignored
- streaming: beta
+ streaming: GA, 40% lower latency
→ “Acme's v4 makes streaming the default” triggered on your blog

Letter builds a marketing struct from your company's context.

Put in your URL. Letter reads your positioning, plans the primitives that fit, builds the whole instance, and hands it back with API and MCP hooks.

https://
  1. crawl
  2. context
  3. plan
  4. apply
  5. hooks
letter plan acme.dev
reading acme.dev … 38 pages, brand, pricing, docs

~ context acme.dev                positioning · 4 offerings · 6 competitors
+ phantom "acme-review.com"       3 posts / week · autopilot
+ kernel  "acme-house-voice"      bar 8.0 · 3 evals
+ trace   24 prompts              4 engines · daily
+ seer    github_release          gated on positioning
+ lede    endpoint                in-brand openers
+ mailer  3 × acme-mail.com       warming · 10 days

Plan: 6 to add, 1 to read, 0 to destroy.
Apply complete. Instance live in 4m 12s.
MCPhttps://app.letterstory.com/api/mcp
RESTPOST /api/integrations/tools/<tool>
CLIletterstory plan acme.dev
Authauthorization: Bearer $LETTER_KEY
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