Configuration reference

Here is each environment variable that the server reads at runtime, in groups. The server reads them at boot. To change one, restart the app.

This list is complete by construction. A test fails the build when config/runtime.exs reads a variable that this page does not document. So the reference cannot drift from the code without a sound.

A few variables refuse to boot on an invalid value. They fall back to no default, and each row says so.

That is deliberate. A typo that quietly turned a bound or a key off would otherwise surface as a bill or a breach. It would not surface as an error message.

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Core

Variable	Default	Required	Effect
DATABASE_URL	—	prod	The Postgres connection string. Boot fails without it.
SECRET_KEY_BASE	—	prod, to serve	Signs and encrypts the session cookies and the tokens. Generate one with openssl rand -base64 48.
MASTER_SECRETS_KEY	—	prod	Wraps each tenant's data-encryption key. Read the secrets model. It is 32 bytes, url-safe base64, with no pad character: openssl rand 32 | base64 | tr '+/' '-_' | tr -d '='. Lose it and you lose each stored secret. Boot refuses a malformed value.
PUBLIC_URL	—	prod	The base URL that the outside world sees, with the scheme. A prod instance refuses to boot without it, or without the deprecated FOUNTAIN_DOMAIN. The old http://localhost:4000 fallback quietly put localhost links in each verification email. This variable builds each link that leaves the app, which is the verification and reset emails and llms.txt. Fountain passes it to each sandbox as FOUNTAIN_BASE_URL. An https:// value also starts the HTTPS redirect, HSTS and the secure cookie flag, and Fountain derives all three from the scheme.
PHX_HOST	The host of PUBLIC_URL.	—	The bare host for the endpoint URL and for the LiveView origin check. Set it only when it differs from the host in PUBLIC_URL.
FOUNTAIN_DOMAIN	—	deprecated	The old combined variable. Fountain still honours it as a fallback for both of the two above. Prefer PUBLIC_URL and PHX_HOST.
PHX_SERVER	true in the shipped image.	—	A 1, true or yes starts the web listener. A release task runs with PHX_SERVER=false … eval '…'. That boots the app, and binds no port.
PORT	4000	—	The HTTP port to listen on.

Database

Variable	Default	Required	Effect
DATABASE_SSL	true	—	TLS to Postgres. Set false for a stock postgres container, which serves no TLS.
DATABASE_SSL_VERIFY	off.	—	Unset, the driver encrypts the connection and verifies no server certificate. true verifies it, against the OS trust store, unless you give a CA file.
DATABASE_SSL_CA_FILE	The OS trust store.	—	The CA bundle to use when DATABASE_SSL_VERIFY=true.
POOL_SIZE	10	—	The size of the database connection pool.
MIGRATE_ON_BOOT	true	—	Whether a release runs the migrations that are due before it serves. A false, and also 0 or no, makes the pod serve and no more. Use that for a deployment that runs the migrations once, in a Job. Read migrations in a Job. bin/migrate always migrates, whatever you set here. Nothing checks that the Job ran. A pod that skips the migrations boots against a database nobody migrated. It then fails on the first query.

Sandboxes

Variable	Default	Required	Effect
SPRITES_TOKEN	—	For conversations.	The platform token for sprites.dev. The app boots without it, and each conversation then fails. Never show it to a tenant, because it pays for each sandbox.
SPRITES_BASE_URL	https://api.sprites.dev	—	Repoints the sandbox API. Whatever you point it at must implement the same contract, and Fountain bundles no alternative.
SPRITES_TIMEOUT_MS	30000	—	Bounds each HTTP call to the Sprites API. A long command, such as a package install or a clone, sets its own timeout for that call. Boot refuses a value that is not positive.
SANDBOX_PROVIDER	sprites	—	Which backend a new sandbox runs on. One of sprites, e2b, daytona and runner. A hosted provider turns on when its credential is there. Boot refuses an explicit default whose credential is absent. A sandbox that already exists stays on the provider Fountain made it on.
SANDBOX_RUNNERS_ENABLED	true	—	A self-hosted runner needs no credential. A false hides the runner provider, and refuses a fountain runner connection.
BROKER_URL	—	—	The management API of an Agent Vault egress broker, for example http://agent-vault:14321. Blank turns credential brokerage off, and each conversation then provisions as before. Set it, and boot also requires BROKER_TOKEN and BROKER_PROXY_URL. This is ADR 0019 gate 1a. It brokers GITHUB_TOKEN and GH_TOKEN only, for the tenants in BROKER_TENANTS only.
BROKER_TOKEN	—	With BROKER_URL.	A session token of an Agent Vault member. Fountain uses it to create a vault, to load credentials and to mint a proxy session for each conversation.
BROKER_PROXY_URL	—	With BROKER_URL.	The proxy address a sandbox dials, for example http://broker.example.com:14322. It is not the same as BROKER_URL when the sandboxes are on a different network from Fountain. Its host is the one host a brokered sandbox may reach.
BROKER_TENANTS	—	—	A comma separated list of user ids. Fountain brokers the conversations of these users. All other users provision as before. This is the operator ratchet of ADR 0019, and it is not a tenant setting.
BROKER_SESSION_TTL_SECONDS	21600	—	How long a proxy session token lives. Fountain mints a new one on each provision and each reattach, and again before a turn when the current one is near its end. Agent Vault accepts 300 to 604800.
BROKER_LOG_RETENTION_HOURS	168	—	How long a conversation's vault on the broker keeps its request log after the conversation ends. GET /api/conversations/:id/egress reads it. A daily job deletes older vaults. Keep it at or below the broker's own log retention.
BROKER_ALLOW_UNENFORCED	false	—	A true lets a brokered conversation run on a provider that has no network policy, for example a self-hosted runner. The sandbox then holds placeholders and a proxy address, but nothing stops a process from a direct connection that avoids the proxy. For development only.
E2B_API_KEY	—	For the e2b provider.	The E2B API key. Its presence turns the provider on.
E2B_BASE_URL	https://api.e2b.app	—	Repoints the E2B control plane.
E2B_TEMPLATE	base	—	The template that Fountain creates a new E2B sandbox from. The stock base template has no agent CLI, so build one from images/e2b/ for real use.
E2B_USER	sprite	—	The in-guest user that envd runs a command as. An images/e2b/ template creates sprite. Set it to user when you point at the stock base template.
DAYTONA_API_KEY	—	For the daytona provider.	The Daytona API key. Its presence turns the provider on.
DAYTONA_API_URL	https://app.daytona.io/api	—	Repoints the Daytona API, for a Daytona you host yourself.
DAYTONA_SNAPSHOT	The org default.	—	The snapshot, which is an image, that Fountain creates a new Daytona sandbox from. The organization must hold it. The default image has no agent CLI, so build one from images/daytona/ for real use.
SANDBOX_IDLE_TIMEOUT_MINUTES	60	—	No turn activity for this long, and Fountain parks the sandbox. A provider without :suspend destroys it instead. The conversation stays resumable either way. A 0 turns the bound off, and boot refuses whatever is not a non-negative integer.
SANDBOX_MAX_LIFETIME_HOURS	0 (off)	—	A ceiling on one continuous run, whatever the activity. Off by default: nothing stops a sandbox that stays busy. Set it to park a persistent home, or destroy an ephemeral sandbox, after this many hours. The same boot refusal applies.
CHECKPOINT_CREATION_ENABLED	false	—	Set to true, and Fountain takes a checkpoint of each persistent home when it parks, on a provider that has checkpoints (Sprites). The checkpoint belongs to that one machine. It can roll the machine back, and it cannot rebuild a machine that the provider lost. Each park adds one checkpoint, and Fountain does not delete old ones. The same flag also makes Fountain checkpoint each environment after it provisions a sandbox, which Sprites cannot restore into a new sandbox.
LOG_OUTPUT_BUDGET_MB	50	—	The durable log volume for one conversation. Once a conversation has persisted this much sandbox output, Fountain writes one truncation marker and discards the rest. Retention bounds age, and this bounds rate. The same 0 rule and the same boot refusal apply.

Webhooks

Variable	Default	Required	Effect
WEBHOOKS_ENABLED	true	—	A false stops every outbound webhook. An endpoint stays saved and gets nothing. Use it on a deployment with no outbound egress.
WEBHOOK_ALLOW_HTTP	false	—	A true lets an endpoint URL use plain http://, for a receiver on your own network. It relaxes the scheme rule alone. Fountain refuses a loopback, link local or RFC1918 target either way, at every request.

Registration and accounts

Variable	Default	Required	Effect
REGISTRATION_ENABLED	true	—	A false closes signup entirely. Somebody will find an open instance on the public internet.
REGISTRATION_ALLOWED_EMAIL_DOMAINS	any	—	A comma-separated list. Fountain refuses a signup outside these domains. Empty means no restriction.
UNVERIFIED_PRUNE_AFTER_DAYS	30	—	Fountain deletes an account that never verified its email after this many days. Such an account can sign in and reach nothing, so it is a row and not a user. A 0 turns the sweep off.
UNVERIFIED_PRUNE_EXEMPT	—	—	Comma-separated email substrings that the sweep never prunes. Use it for an operator or test account that stays unverified on purpose.
SECRET_EXPIRY_NOTICE_DAYS	7	—	Days before a vault secret's recorded expiry that Fountain emails the owner. The vault page shows an amber badge for the same window. A 0 turns the notice off.
FIRST_USER_ADMIN	false	—	A true promotes the first account that becomes verified to admin, while the instance has no admin. The audit trail records it (ADR 0011). Leave it off on a multi-tenant deployment, because it hands admin to whoever verifies first.

Email

Production refuses to boot unless you configured exactly one of the three delivery options. A verification email that Fountain throws away leaves signup at a dead end, with no error to see. Read Email.

Variable	Default	Required	Effect
RESEND_API_KEY	—	One of three.	Resend delivers the mail.
SMTP_HOST	—	One of three.	Any SMTP server delivers the mail.
SMTP_PORT	587	—	The SMTP port.
SMTP_USERNAME	—	—	Omit it for a relay that wants no authentication.
SMTP_PASSWORD	—	—
SMTP_TLS	always	—	STARTTLS by default. Use never for a relay on a trusted network that does not offer it.
EMAIL_DELIVERY	—	One of three.	A none turns email off, on purpose. An account then self-verifies at registration (ADR 0011). Nothing can deliver a password-reset email. So in this mode, a password that somebody forgets stays forgotten.
EMAIL_FROM	—	When mail is on.	The From address. A real delivery provider needs it. A prod instance refuses to boot without it, because a receiver rejects mail from a domain nobody verified anyway. EMAIL_DELIVERY=none uses it for nothing.
SUPPORT_EMAIL	—	—	Where "contact support" in an account email points. Those are the suspension and deletion emails. Fountain also mails a POST /api/support/reports report there. Unset, the copy names no address, and Fountain mails no report.
SUPPORT_GITHUB_REPO	—	—	An owner/repo. Each support report also becomes a GitHub issue there, with the labels support and the category. It needs SUPPORT_GITHUB_TOKEN.
SUPPORT_GITHUB_TOKEN	—	—	A token with issues:write on SUPPORT_GITHUB_REPO.

Authentication

Variable	Default	Required	Effect
GITHUB_OAUTH_CLIENT_ID	—	—	Turns the GitHub sign-in button on. Unset, Fountain hides the button, and email and password auth still works.
GITHUB_OAUTH_CLIENT_SECRET	—	—
GOOGLE_OAUTH_CLIENT_ID	—	—	Turns the Google connection on, for accounts the egress broker is on for. A tenant connects Gmail once on the Connections page, and Fountain keeps the refresh token. Register a Web client in Google Cloud with the redirect URI <PUBLIC_URL>/connections/google/callback, and enable the Gmail API. Unset, the page says the feature is not configured.
GOOGLE_OAUTH_CLIENT_SECRET	—	—

Payment

Variable	Default	Required	Effect
CREDITS_ENABLED	false	—	Credits on. Off by default: on a self-hosted instance there is nothing to sell. On, every account holds a credit balance, turns and contacts burn it, and a zero balance refuses new work.
BILLING_ENABLED	—	—	The old name of CREDITS_ENABLED. Fountain reads it for one release and writes a warning at boot. CREDITS_ENABLED wins when you set both.
STRIPE_SECRET_KEY	—	For billing.	The Stripe API key.
STRIPE_WEBHOOK_SECRET	—	For billing.	Verifies the signature on a POST /api/stripe/webhook.
PROVIDER_HOURLY_CENTS	—	No.	What you pay each sandbox provider, in cents per sandbox hour, as sprites=10.76,e2b=5.45. Rates can be fractional. A provider you leave out stays unpriced.
PROVIDER_COST_BASIS	active	No.	Which hours the provider rate multiplies. An active counts every hour a sandbox was awake. A turn counts only the hours with a prompt in flight. Use turn where the provider drops to near-zero between prompts.
AGENTMAIL_INBOX_CENTS	—	No.	What AgentMail charges for one inbox each month, in cents.
AGENTPHONE_NUMBER_CENTS	—	No.	What AgentPhone charges for one number each month, in cents.
AGENTMAIL_MESSAGE_CENTS	—	No.	What AgentMail charges for one email, in cents. Give the fraction, such as 0.2 for $2 per 1,000 emails. A whole number rounds this rate to zero.
AGENTPHONE_MESSAGE_CENTS	—	No.	What AgentPhone charges for one SMS, in cents. Fountain counts an inbound message too, because AgentPhone charges for it.
SANDBOX_RESERVE_CENTS	200	No.	The credit one live sandbox needs in the balance. A tenant may run balance / reserve sandboxes at once, between the floor and the ceiling.
SANDBOX_CAP_FLOOR	2	No.	The fewest sandboxes a tenant with a positive balance may run at once.
SANDBOX_CAP_CEILING	20	No.	The most sandboxes one tenant may run at once, unless an admin override raises it.
SANDBOX_FLEET_CEILING	20	No.	The most live sandboxes across every tenant. Set it to what your sandbox provider plan allows. A start beyond it gets 503 fleet_full.
CREDIT_OPENING_CENTS	500	No.	The credit a new account starts with, in cents.
CREDIT_OPENING_DAYS	14	No.	How many days the opening credit lasts.
TEAM_CONTACT_CEILING	10	No.	The most teammate contacts one account may hold at once.
CREDIT_TURN_HOUR_CENTS	25	No.	What a tenant pays for one hour of turn time, in whole cents, from their prepaid balance.
CREDIT_NUMBER_CENTS	—	No.	What a tenant pays for one phone number each month, in whole cents. Unset means the number burns nothing.
CREDIT_INBOX_CENTS	—	No.	What a tenant pays for one inbox each month, in whole cents. Unset means the inbox burns nothing.
CREDIT_EMAIL_MESSAGE_CENTS	—	No.	What a tenant pays for one email, in whole cents. Unset means an email burns nothing.
CREDIT_SMS_MESSAGE_CENTS	—	No.	What a tenant pays for one SMS, sent or received, in whole cents. Unset means an SMS burns nothing.
CREDIT_PACKS_CENTS	1000,2500,10000	No.	The credit packs a tenant can buy, in cents, as a list.

The rate variables are different from every other price here. They are what you pay, not what a tenant pays, and no other part of Fountain knows them. The admin finance panel at /admin/finance holds them next to your revenue, per tenant. The panel switches between the two hour bases per view. Compare both totals against a real invoice, then keep the basis that matches.

Each rate can be fractional. Per-message rates usually are, and a whole number rounds them to zero.

Set none of them and the panel still works. It shows hours, inboxes, numbers and message counts, and it shows — in each money column. A rate you do not set stays — and never becomes $0, because a cost of zero and a cost nobody told us about are different facts.

Public pages

The / page is not the same page on every deployment. The Fountain project's own site shows the product page, with the prices and the opening credit. Every other deployment shows a plain front door: the name, a way in, and a link to this manual.

Your deployment is not the Fountain project, so the front door is the default.

Variable	Default	Required	Effect
PRODUCT_NAME	Fountain	—	The name the console, the sign-in page, the OAuth consent screen and each email subject use for this deployment. Set it when you sell a hosted deployment under a different brand. The CLI, the API and this manual keep the name Fountain, because that is the name of the engine. When the two differ, each manual page opens with one line that says so.
MARKETING_SITE	false	—	A true serves the Fountain project's product page at /. It also puts the project's copyright line in the footer. Turn it on only if you operate the project's own site.

Legal pages

These four variables carry the identity that /terms and /privacy render. That is the operator's identity, and not the Fountain project's.

Set all four, or set none. A partial set refuses to boot. With none set, the two pages return 404, and their links disappear from signup and the footer.

There is one exception. With payment turned on, the pages stay up and carry loud {{...}} placeholders until you configure them. An instance that charges money must publish terms.

Variable	Default	Required	Effect
LEGAL_ENTITY	—	No.	The legal entity that operates this instance, such as Example Corp Inc.
LEGAL_CONTACT_EMAIL	—	No.	The contact address that both pages show.
LEGAL_JURISDICTION	—	No.	The law and the venue that govern, such as the State of Delaware, USA.
LEGAL_EFFECTIVE_DATE	—	No.	The "Last updated" date on both pages.

Proxies and origins

Variable	Default	Required	Effect
TRUSTED_PROXIES	—	Behind a proxy.	Comma-separated CIDRs that Fountain steps over as it resolves the client IP from X-Forwarded-For. Without it, the rate limit for each IP collapses into one bucket keyed on the proxy. Set it too broad, and a client can spoof its way past the rate limit.
CHECK_ORIGIN_EXTRA	—	—	Comma-separated extra origins that can open a LiveView websocket. Fountain always includes your own host.
OAUTH_CLIENTS	—	—	A JSON array of {id, name, redirect_uris}. It names the browser apps that can "Sign in with Fountain". That is OAuth code with PKCE, for a public client, and decisions/0021 covers it. A redirect URI must match exactly. Unset means none.
API_CORS_ORIGINS	—	—	Comma-separated browser origins, or a *, that can call /api with a bearer key from another site. A standalone client such as the team app needs that. It is off when unset, and a cookie never crosses an origin either way.
CONVERSATIONS_APP_URL	https://jakegaylor.com/fountain-conversations/	—	Where the console sends a person to watch a conversation. The default is a static build that takes your Fountain's URL as input. So it works for a self-hosted server as soon as API_CORS_ORIGINS admits https://jakegaylor.com. Point it at your own copy instead, or set it to "" to say this deployment has no such app.
TEAM_APP_URL	https://jakegaylor.com/fountain-team/	—	The same, for the team roster.

Clustering

You need this for more than one replica, and for nothing else. Read Clustering for what breaks without it.

Variable	Default	Required	Effect
CLUSTER_DNS_QUERY	—	Multi-replica.	The DNS name that Fountain polls to discover a peer. In Kubernetes that is a headless service. Empty or unset, the cluster is off.
RELEASE_NAME	Set by the release.	—	The node basename that peer discovery uses. It must match what each node registered as. The release sets it, so override it only when you know why.
DNS_CLUSTER_QUERY	—	—	A second, separate discovery mechanism, which is Phoenix's DNSCluster. Leave it unset when you use CLUSTER_DNS_QUERY.

Observability

Variable	Default	Required	Effect
METRICS_PORT	9568 in prod, off elsewhere.	—	The private Prometheus listener, which serves /metrics and /health. A "" or a 0 turns it off. Keep it off the public internet.
SENTRY_DSN	—	—	Turns error reports on. Unset, the SDK is inert and nothing leaves the instance. It accepts sentry.io, or any endpoint that speaks the Sentry API, such as GlitchTip.
SENTRY_ENVIRONMENT	The build env.	—	The environment tag on a reported error.
FOUNTAIN_BUILD_SHA	Set by the image build for a release image, or by the deployment for a main-line image.	—	Matches an error and a trace to a deploy. The app footer shows it too.
OTEL_SERVICE_NAME	fountain	—	The service name on an exported trace.
OTEL_EXPORTER_OTLP_ENDPOINT	HONEYCOMB_ENDPOINT	—	The OTLP target for a trace export, over HTTP with protobuf.
OTEL_EXPORTER_OTLP_HEADERS	—	—	The key=val,key=val headers on a trace export.
HONEYCOMB_ENDPOINT	https://api.honeycomb.io	—	The Honeycomb shortcut for the endpoint above.
HONEYCOMB_API_KEY	—	—	The Honeycomb shortcut that adds the x-honeycomb-team header.

Fountain configures a trace export in production, while it serves, and nowhere else. It is off by default. It exports a span only when you explicitly set OTEL_EXPORTER_OTLP_ENDPOINT, HONEYCOMB_ENDPOINT or HONEYCOMB_API_KEY.

The OTel SDK also honours its own standard variables, and those win. Set OTEL_TRACES_EXPORTER=otlp or =none to force the export on or off, whatever the table above says.

Hosted Buzz agents

Fountain can host the buzz-acp harness for a Buzz agent (ADR 0020). A Buzz agent then keeps a body on its relay, with no desktop up.

The image bakes the harness binary in, for both amd64 and arm64. These two variables tune where it runs, and how its ACP child reaches back. An operator rarely sets either one, because the defaults are correct for the packaged image.

Variable	Default	Required	Effect
BUZZ_ACP_BASE_URL	The loopback endpoint, http://127.0.0.1:$PORT.	—	The base URL that the harness's ACP child, fountain acp, uses to reach this instance. It defaults to the loopback, so harness traffic never leaves the pod. Override it only to point the child at a different Fountain endpoint.
FOUNTAIN_CLI_PATH	/usr/local/bin/fountain	—	The path to the fountain CLI that the harness runs as its ACP child. The image bakes it at the default, so override it only for a layout that is not standard.

Upstream publishes buzz-acp for amd64 alone. So Fountain builds it for both architectures from source, and bakes it in. Read .github/workflows/buzz-acp-publish.yml.

Feature flags

PostHog evaluates a per-user flag, Fountain.FeatureFlags, when you set a project key. Fountain caches an answer for one minute for each user.

When PostHog is unreachable, Fountain reuses the last answer it gave. With no answer at all, each flag reads off, so an outage never turns a feature on. Without PostHog you can force a flag on for each user.

Variable	Default	Required	Effect
POSTHOG_PROJECT_API_KEY	—	—	The PostHog project API key. That is the public phc_… token, and not a personal key. Unset, Fountain looks up no flag remotely.
POSTHOG_HOST	https://us.i.posthog.com	—	The PostHog ingestion host. Use https://eu.i.posthog.com for EU Cloud, or an instance you host yourself.
FEATURE_FLAGS_ON	—	—	Comma-separated flag keys, forced on for each user, such as team_comms. It wins over PostHog.

Product analytics

The same project key sends product events to PostHog. Fountain captures most of them on the server.

Set no key and Fountain sends nothing. Set a key and the events go to your own PostHog project.

Fountain captures an event at three points in the code. Each point is a function that the operation must call, so Fountain captures a new action without a new call site.

• Every audited change, under the name of its audit action. agent.created and vault.secret.write are examples.
• Every usage event that the meter records, with a usage. prefix. usage.turn_started is an example.
• The end of a conversation turn, as conversation.turn.done, conversation.turn.failed or conversation.turn.interrupted.

Each API write leaves a second audit row named after the request line. Fountain sends these rows as one event, api.request. The route is a property, not part of the name. A name per route makes an event type per route, and each event type fills the list that every person on the project reads. A property keeps the count of names at one, and PostHog can break down a property.

The api.request event carries method, route, status and status_class. Together they answer which endpoints your callers use, and which of them fail. A request that Fountain refuses before it knows the account has no person, so Fountain sends no event for it. The audit trail keeps that row.

One kind of audited change stays out of PostHog. The audit trail keeps it. It is an API key that Fountain issued to itself. A sandbox and a Buzz harness each get a key, and an OAuth token is a key. These were 70 percent of the trail in one day. Fountain keeps a key that a person makes in the console, or through the API.

Fountain also captures $pageview for each console page, $identify when the shape of an account changes, and $feature_flag_called when it reads a flag. Each event carries the flags that Fountain already knows for that person, as $feature/<key>.

Web analytics

The public pages load the PostHog browser library. These pages are the home page, the legal pages, the manual and the sign-in flow. The console loads no browser library, and Fountain captures console pageviews on the server.

The split has a reason. A pageview from the server has no session, no referrer and no device. Fountain also drops an event with no account, so a visitor with no account is invisible to it. Only a browser knows these facts, and only the public pages have visitors who are not yet accounts.

The browser library sends anonymous events. It makes no person profile for a reader. A person profile appears when an account appears.

PostHog records the public pages

PostHog session replay makes a record of each visit to a public page. The record covers the home page, the legal pages, the manual and the sign-in flow.

PostHog does not record the console. This includes the dashboard, the agent and vault pages, and the admin pages. The console loads no browser library, so there is no recorder on those pages.

Fountain masks every input in the record. This matters on the sign-in and sign-up pages, where the mask hides the email address. PostHog masks a password field in all conditions.

The switch for replay is a PostHog project setting, not a Fountain setting. To stop the records, turn replay off in your PostHog project. To stop the browser library and the records together, set POSTHOG_BROWSER_CAPTURE to false.

Fountain joins the two halves at sign-in. It reads the anonymous id from the PostHog cookie, and it tells PostHog to merge that visitor into the account. The pages a person read before the account then belong to the account. Fountain reads this cookie and writes nothing to it. A reader with no cookie signs in as normal, and Fountain sends no merge.

Each browser event carries surface: "public". Each console pageview carries surface: "console". Use this property to hold the two apart.

Fountain adds the PostHog origins to the Content Security Policy of the public pages. The console keeps its own policy, which names no PostHog origin. Fountain reads POSTHOG_HOST for both origins. PostHog Cloud serves the library from a second origin, and Fountain derives that origin from the first.

Fountain sends no secret value, no environment variable value, no prompt and no agent output. An event holds the name of the action, the type of the resource, and counts or sizes.

Delivery is best-effort. Events go to a queue and leave in batches. Fountain drops them if the queue is full or if PostHog answers with an error, and it counts each drop on the fountain.analytics.dropped telemetry event. An analytics failure cannot fail the operation it measures.

Variable	Default	Required	Effect
POSTHOG_CAPTURE	true	—	Set it to false to stop product events. Flag evaluation continues.
POSTHOG_BROWSER_CAPTURE	true	—	Set it to false to keep the PostHog browser library off the public pages. This also stops the session recordings. Server capture continues.
POSTHOG_PERSON_PII	true	—	Set it to false to keep the account email out of PostHog. The person is then known by user id alone.
POSTHOG_INSTANCE	PHX_HOST	—	The name of this deployment. Each event is a member of this PostHog group, so two deployments that report to one project stay apart.

Teammate email and phone

Behind the team_comms flag, you can give a teammate an email address, from AgentMail, and a phone number, from AgentPhone. The teammate then gets MCP tools to send and read on both.

Fountain holds the provider keys and serves the tools itself, so a key never enters a sandbox. With either key unset, the feature reports itself unavailable, even where the flag is on. GET /api/team/comms reports that state, and POST /api/team/:agent_id/contact provisions a contact. Read Team.

Variable	Default	Required	Effect
AGENTMAIL_API_KEY	—	—	The AgentMail API key. Fountain creates a teammate inbox under it.
AGENTMAIL_BASE_URL	https://api.agentmail.to	—	The AgentMail API host. Use https://api.agentmail.eu for the EU region.
AGENTMAIL_DOMAIN	—	—	A custom domain that you verified, for a teammate address. Unset, Fountain uses AgentMail's shared domain.
AGENTPHONE_API_KEY	—	—	The AgentPhone API key. Fountain provisions a teammate number under it.
AGENTPHONE_BASE_URL	https://api.agentphone.ai	—	The AgentPhone API host.
AGENTPHONE_WEBHOOK_SECRET	—	—	The secret that AgentPhone returned when somebody pointed the account's master webhook at POST /api/webhooks/agentphone on this instance. It verifies an inbound delivery. A text to a teammate's prompt_from_number then becomes a prompt in its conversation. Unset, the endpoint answers 503 and processes nothing inbound.