querying-canvas-data

Querying canvas data

The ph bridge is the only way a canvas talks to PostHog. Import it with import { ph } from "@posthog/canvas-sdk" — a platform-provided module, so it needs no dependencies entry. The same object is also installed as the window.ph global, which existing canvases use; prefer the import in new code. Its typed surface is references/canvas-sdk.d.ts. Never initialize it: credentials stay in the host, and fetch(), posthog-js, and hand-rolled clients cannot reach PostHog from the sandbox. External requests and resources require a non-PostHog origin declared in capabilities.network.origins, and work only in the published canvas — the edit-mode preview blocks all direct network access. This includes external stylesheets; remote scripts remain blocked.

Data hierarchy — back every metric with a saved insight

1. Preferred — save an insight, load it by reference. Use the PostHog MCP insight tools to

create/save an insight that computes the metric with an insight query type (TrendsQuery, FunnelsQuery, RetentionQuery, PathsQuery, or the web-analytics kinds WebOverviewQuery / WebStatsTableQuery — not raw SQL). Confirm its numbers, note the short_id, and render it with await ph.loadInsight(shortId, { dateRange }). These are proven queries — numbers match the PostHog UI exactly (sessionization, unique users, breakdowns, bounce rate). Never fabricate a query or guess event/property names; discover and save them via MCP first.

1. Secondary — an ad-hoc typed node: ph.query({ kind: "TrendsQuery", series: [...], dateRange: {...} })

when saving an insight genuinely doesn't fit.

1. Last resort — inline HogQL: ph.query("SELECT …"), only when no insight kind can express

the metric; you then own the SQL and its date window.

For web-analytics boards specifically, use the web-analytics query kinds — raw HogQL subtly gets bounce rate, sessionization, channel attribution, and unique-visitor counts wrong.

Whatever tier you use, declare it in the project's `capabilities` before publishing: every ph.loadInsight short id in capabilities.posthog.insights, every ph.capture event name in captureEvents, and inlineQueries: true for any ph.query use. The host rejects undeclared calls at runtime, and validation fails on undeclared literals.

Verifiability — every claim must be checkable in PostHog

A number a viewer cannot verify is a number they cannot trust. Every data-backed figure a canvas shows — a KPI, a chart, a table, a stated conclusion — must carry the verification affordance for its tier:

1. Insight-backed metrics link the real insight in PostHog. For a metric loaded from a saved

insight (the preferred tier), render a "View in PostHog" affordance that calls ph.openExternal(insightUrl) from a click. Mint the URL at authoring time with the generate-app-url MCP tool (path template /insights/{id} with the insight's short id) and bake the returned URL into the source verbatim — never hand-build one. ph.openExternal only opens https://*.posthog.com URLs and only from a user gesture, so wire it to a button or link, never to load or render. Do not also bake the insight's saved query text into the source: canvas source is readable by every canvas viewer, while access to the insight itself is enforced by PostHog — the link is where a viewer inspects the query, with their own permissions applied.

1. Ad-hoc queries disclose the exact query that ran, viewable in place. For a figure computed

by ph.query (a typed node or inline HogQL), show the query behind it — the HogQL text, or the typed query node pretty-printed as JSON — in a modal or a collapsed disclosure attached to the card (a Quill Dialog or Collapsible in a React canvas, a <details> element in an HTML one). Render it from the same constant or builder you pass to ph.query, so the displayed query can never drift from the executed one. This discloses nothing beyond what the viewer already runs: ph.query executes as the signed-in viewer.

These are not optional polish: a canvas that presents PostHog data without them is incomplete. Keep the affordances compact — a small link icon per insight-backed card, a "View query" disclosure per ad-hoc card, or one shared modal listing every ad-hoc query the canvas runs, each labeled with the figure it backs.

For a status board, set refresh to the cache lifetime in seconds. Use a whole number from 30 to 86400 (one day); values outside that range, or fractional ones, fail at runtime:

await ph.loadInsight(shortId, { refresh: 30 })
await ph.query(queryNode, {}, { refresh: 30 })

Result shapes — read them correctly or every value renders 0

• Trends-style results (insight query types, via ph.loadInsight or a typed node): results

is an array of series objects, not rows. Each series has data: number[] (per interval), days: string[] (ISO), labels: string[], count (sum), aggregated_value (single-value total), label, and optional compare_label: "current" | "previous". A KPI total is results[0].count (or .aggregated_value); a line chart plots results[0].data over results[0].days. count sums the per-interval values, which double-counts a unique-users series (math: "dau") for anyone active on several days — for a period-unique KPI, set trendsFilter: { display: "BoldNumber" } on the query and read aggregated_value instead. With a compare period, find the prior series by compare_label === "previous" — never by index. columns is empty here.

• SQL results: { columns: string[], results: rows[][] } — each row an array of cell values in

columns order.

Load progressively — render each section when its own data lands

PostHog queries can take several seconds each, and a board usually runs several. Never gate rendering on all of them:

• Fire independent queries concurrently on mount; never chain unrelated queries with sequential

awaits. The host caps a canvas at 8 in-flight data requests and rejects the ninth ("Canvas data request exceeds runtime limits") rather than queuing it — a board that needs more than 8 consolidates them (one query returning every row, sliced client-side) or throttles the overflow behind a small concurrency limiter, still with one state per section.

• Give every query its own { loading, error, data } state and let each card, chart, or table

swap its skeleton for data the moment its own result arrives. One shared loading flag or a single Promise.all across independent queries makes the fastest metric wait for the slowest — the canvas must fill in progressively, not appear all at once.

• Render the static chrome (heading, date picker, card frames with skeletons inside) immediately;

only the value inside each section waits for its query.

• Defer queries the first paint doesn't need: content behind a tab, a collapsed section, or a

drill-down runs its query when the user reveals it, not on mount.

Load data in useEffect with useState, and aggregate in the query; never fetch raw event dumps. Treat a rejected query and an empty result as different states: .catch must set an error state that renders visibly (message + retry), never fall through to zeros, an empty chart, or a "no data" message — a swallowed error makes real breakage (a missing table, an auth failure) look like missing data. Reserve the empty state for a query that succeeded with no rows.

Date windows

• Pass the canvas's date-picker window straight into dateRange:

ph.loadInsight(shortId, { dateRange: { date_from: win.start.toISOString(), date_to: win.end.toISOString() } }) — the saved insight re-scopes to the window with no time SQL. Typed nodes take the same dateRange. Re-run every query when the window changes.

• A saved SQL insight may ignore dateRange (its window lives inside the SQL) — a reason to

prefer insight query types. If its window comes from a {variables.…} placeholder, drive it through variables (below) instead; dateRange will never reach it.

• Inline HogQL escape hatch only: never bake now() or a hardcoded INTERVAL. Compute unix bounds

(Math.floor(win.start.getTime() / 1000)) and write half-open timestamp >= toDateTime(fromUnix) AND timestamp < toDateTime(toUnix). Prior period = the equal-length window immediately before; bucket with toStartOfDay/toStartOfHour.

SQL variables

A saved SQL insight whose HogQL contains {variables.name} placeholders takes its values per call, keyed by the variable's code name (not its uuid):

await ph.loadInsight(shortId, { variables: { product: 'surveys', month: '2026-07-01' } })

This is how one saved insight fills a whole board — the same per-product insight loaded once per product — rather than every tile resolving the insight's saved default.

• Read the code names off the insight's query first (insight-get over MCP). The host rejects a

variable the insight doesn't use, and rejects one whose value didn't take effect, instead of silently falling back to the saved value — so a variable mismatch surfaces as a visible error, not as another product's numbers.

• Variables are part of the read cache key, so N products means N loads. Prefer one insight

returning every product as rows over the same insight loaded N times, and slice it client-side.

• Values are typed by the variable's definition in PostHog (String / Number / Boolean / Date / List);

pass the same shape the insight expects, and an array for a multi-select List variable.

Live Tasks data

For a task inbox, queue, or status board, query system.tasks and system.task_runs through ph.query. Do not call posthog:tasks-list while authoring and embed its response: that produces a snapshot, while the system tables keep the rendered canvas live.

The tables run as the signed-in viewer. They are project-scoped and require access to the Tasks resource. system.tasks includes only non-internal tasks filed in live public spaces; it excludes private, personal, unfiled, and internal tasks. Always exclude soft-deleted tasks explicitly.

Join a task to its latest run when the canvas needs current status:

const data = await ph.query(`
  SELECT
    t.id,
    t.task_number,
    t.title,
    t.repository,
    t.created_by_id,
    t.created_at,
    t.updated_at,
    latest.status AS latest_run_status
  FROM system.tasks AS t
  LEFT JOIN (
    SELECT
      task_id,
      argMax(status, tuple(created_at, id)) AS status
    FROM system.task_runs
    GROUP BY task_id
  ) AS latest ON latest.task_id = t.id
  WHERE t.deleted = 0
  ORDER BY t.updated_at DESC
  LIMIT 100
`)

This is inline HogQL, so declare capabilities.posthog.inlineQueries: true. Render links with ph.navigate.toTask(id) rather than constructing task URLs.

Do not promise filters the tables cannot express. channel_id is not queryable, so a canvas cannot currently restrict this query to its own space. Filtering to the current viewer also requires a known numeric user id; the canvas runtime does not inject one. State these limits when the request depends on “this space” or “my tasks” instead of silently showing project-wide public tasks.

Runtime memory — ph.state

Durable key-value storage per canvas. Declare every scope you use in capabilities.posthog.state (["user"], ["shared"], or both) — undeclared scopes fail validation and the host refuses them at runtime. Scope "user" (the default when no scope is passed) is private to each viewer; "shared" is one value per canvas, visible to the whole team.

const draft = await ph.state.get('draft') // user scope by default; null when unset
await ph.state.set('draft', { text }) // JSON value, capped at 64 KB serialized
await ph.state.set('draft', null) // null deletes the key
await ph.state.set('board', { columns }, { scope: 'shared' }) // team-visible
const entries = await ph.state.list({ scope: 'shared' }) // [{ scope, key, value, updatedAt }]

• Load state in an effect on mount and render a skeleton until it resolves; writes are

last-write-wins, so re-read (or trust your own write) rather than merging.

• 256 keys per scope. Store big data in PostHog (insights, the warehouse) and reference it.
• State is team-visible application data — never secrets, never viewer PII.

When a user asks about a canvas's current progress or settings, do not infer them from source alone. Call canvas-state-retrieve with the canvas id after reading its source. It returns shared state plus the authenticated user's own user-scoped state for canvases in public channels or their personal channel. Use canvas-state-set when the user asks to change those values; read first, preserve unrelated keys, and use the scope the canvas source expects.

Canvas discussions use the generic comment tools. Read them with comments-list filtered to scope=desktop_canvas, the canvas id as item_id, and its discussion_task_id as task_id. Create a root comment or reply with comments-create, using the same scope and ids (put the task id in item_context.taskId). The same public-channel and personal-channel visibility rules apply.

PostHog writes — ph.actions

ph.actions.invoke(verb, payload) writes into PostHog as the viewer. Declare every verb in capabilities.posthog.actions; undeclared or unregistered verbs fail validation and the host refuses them at runtime. Invocations must be wired to an explicit user gesture (a button the viewer clicks) — the host rejects calls made on load or render.

Render the result or the thrown error visibly, and disable the button while the call is in flight — every invocation is a real PostHog write.

The registry is the source of truth for verbs. Before wiring one, list it with the canvases-actions-retrieve tool: each entry carries verb, summary, destructive, and usage — the payload and result shape, what invoking it actually does, and the confirmation copy it warrants. Follow a verb's usage exactly, including what the success message may claim. Do not infer a verb's payload from the matching product's own MCP tools or skills — an MCP tool call (you, now, with your credentials) and a canvas verb (the viewer, later, in the published canvas) differ in payload shape, auth, and behavior. Invoking looks like:

const { result } = await ph.actions.invoke('tasks.create', { title, description })

Side effects

• ph.capture(event, properties?, distinctId?) — analytics events for interactions

(fire-and-forget). Session replay, $session_id, and person attribution are handled by the host automatically; never initialize recording, set session ids, or roll your own capture.

• ph.openExternal(url) — opens https://posthog.com / *.posthog.com URLs only, and only from

a user interaction (opens outside focus are ignored). Sandboxed target="_blank" navigation is blocked, so do not use it as a fallback or link elsewhere.

• ph.navigate.toTask(id) / .toNewTask() / .toCanvas(id) / .toNewCanvas() — in-app

navigation within the canvas's own channel.