# SendLang: A DSL for Email Automation > Source: > Published: 2026-07-15 15:23:43+00:00 # A language layer for lifecycle email SendLang is the home of two small, focused languages. SendQL describes who a message is for. SendFlow describes what happens to them over time — and speaks SendQL natively. Written by people *and by coding agents* — a published grammar, a type checker to iterate against, and a diff you approve. [See how](#agents). SendLang ## One family, two languages SendQL is the noun. SendFlow is the verb. Together they turn contact data and event streams into campaigns you can read in a diff. ### SendQL the whoA segment-definition query language. Every query is a single boolean expression describing which contacts a segment matches. ### SendFlow the whatA drip-workflow language stored in `.flow` files. It reads top to bottom and embeds SendQL for every condition. Why a language ## Your lifecycle email, in version control Every other tool locks your cohorts and lifecycle campaigns inside a visual editor. Make them a language instead, and they become text you can diff, review, and hand to a coding agent. - It lives in version control - Every segment and workflow is a plain text file. Diff it, review it in a pull request, roll it back. Your targeting and your drip logic earn the same rigor as the rest of your code. - It fails before it sends - A misspelled attribute is a type error with a line and a column — not a campaign that quietly sends to nobody for a week. - A coding agent can write it - This is the big one. A canvas is a dead end for an agent; a language is the loop it already works in. Describe the outcome, let it draft the file, merge it once it passes review. Coding agents ## Hand the campaign to an agent A canvas is a dead end for a coding agent — it cannot read it, change it, or tell you what it changed. A language is the loop an agent already works in: read the file, write the file, run the checker, open a pull request. That is not a side effect of the design. It is a reason for it. “Three days before a trial ends, email them. If they have not clicked within three days, send the upgrade offer.” - The docs are machine-readable - Every page has a Markdown twin, and llms.txt / llms-full.txt hand an agent the whole of both languages in a single fetch. Nothing to scrape, nothing to guess at. - A grammar, not a guess - The normative EBNF and the reserved-word list are emitted by the parsers themselves, so the spec an agent reads cannot drift from the code that judges what it writes. - The type checker is the feedback loop - Every parse and type error carries a line, a column, and a message that names the fix. The agent iterates against the checker until the run is clean — and nothing sends until it is. - You are still the approver - No goto, no unbounded loops, nothing to evaluate. The worst an agent can hand you is a workflow that terminates — and you read it as a diff before it ever reaches a contact. The shortest useful thing you can do: put [/llms-full.txt](/llms-full.txt) in your agent's context. That is both languages, complete, in one fetch. [Writing SendLang with a coding agent](/docs/agents) SendQL ## Describe exactly who you mean SendQL reads events as a first-class source alongside contact attributes — the gap left by engines that see only precomputed rollups, never the raw stream. - Attributes and lists - Match on contact data with operators, in [...] sets, contains / starts with / ends with, and list or segment membership. - Events as a first-class source - Query the raw event stream directly — count, exists, sum, avg, last, first — not just precomputed engagement rollups. - Consent and suppression - Express deliverability rules inline: subscribed to "topic", opted out of "topic", unsubscribed from all, not suppressed. - Windows and recency - Bind a time window to any event source with within 30d or between two dates, and reason about recency with now - 14d. The same file, rendered as a canvas - Entercart_updated - Wait1 hour - Sendcart-reminder - repeat up to 2 · every 24h · until orderSendcart-nudge - Exitpurchased SendFlow ## Structure, no goto A workflow reads top to bottom and maps losslessly to a flowchart — sequence, waits, branches, weighted splits, and one bounded repeat. Never a goto, never an unbounded loop. - One trigger, many exits - Enter on a segment, an activity, an email event, or a duration before a contact's own date. Named exits report conversions the moment they happen. - Timed steps - wait 2d, wait until a date or attribute, or wait up to 7d until a condition — with an optional timeout arm. - Branch, split, hold out - Fall-through if / else if / else, weighted split { 30%: ... 70%: ... } that must sum to 100, and hold out 10%. - Bounded loops only - The single loop is repeat up to N every duration until a condition. No goto, no unbounded loops, ever. How they fit ## SendFlow speaks SendQL The predicate you write to define a segment is the very same syntax that drives every condition inside a workflow. A SendQL segment The same predicate, inside a workflow - A strict superset - One shared token stream - One type-checker and diagnostics Design ## Built like languages, not config Both languages are versioned by a profile number, split cleanly from their execution engines, and specified down to a machine-checked grammar. - Structured by design - Sequence, branch, bounded repeat, timed waits, named exits — a control-flow subset that maps losslessly to a flowchart. - Events as first class - Selection over the raw event stream sits alongside contact attributes, so you can segment on behavior, not just state. - Golden-pinned grammar - A normative EBNF is generated from the parser and pinned by tests, so the spec can never silently drift from the code. - Precise diagnostics - Parsing and type-checking are separate stages, and every error carries a line and column pointing at the exact token. - A canonical formatter - SendFlow ships a one-true-layout printer — gofmt for flows — so every workflow in your repository reads the same way. - A canvas, losslessly - The control flow is restricted enough that a workflow maps onto a flowchart and back with nothing lost — comments included. Text and canvas are two views of one thing. Documentation ## The whole language, written down Every construct in both languages, every diagnostic they can produce, and a normative grammar generated from the parsers themselves — so the spec can never quietly drift from the code.