Errors

Every public exception thrown by the SDK extends AlterSDKError. The hierarchy mirrors the Python SDK one-for-one — same class names, same semantics, same fields.

For the canonical error code → exception class mapping and recovery guidance, see Errors.

import {
  NoDelegatedGrantError,
  QuotaExceededError,
  RateLimitError,
  ScopeReauthRequiredError,
} from "@alter-ai/alter-sdk";

const makeRequest = () =>
  app.request("GET", url, { provider: "<provider-id>" });

try {
  await makeRequest();
} catch (error) {
  if (error instanceof NoDelegatedGrantError) {
    const session = await app.createConnectSessionForError(error);
    redirectUser(session.connectUrl);
    return;
  }
  if (error instanceof ScopeReauthRequiredError) {
    // The user must re-authorize with wider provider scopes.
    console.warn(`Missing scopes: ${error.missingScopes?.join(", ")}`);
  }
  if (error instanceof RateLimitError) {
    // A transient throttle. `scope` says WHICH ceiling was hit, which decides
    // the remedy: spreading load across keys helps an `api_key` throttle and
    // does nothing for an `organization` one.
    console.warn(`Throttled on ${error.scope ?? "an unnamed ceiling"}`);
    await new Promise((r) => setTimeout(r, (error.retryAfter ?? 1) * 1000));
    return makeRequest();
  }
  if (error instanceof QuotaExceededError) {
    // Request-quota policy denial — the SDK never auto-retries it.
    await new Promise((r) => setTimeout(r, (error.retryAfter ?? 60) * 1000));
    return makeRequest();
  }
  throw error;
}

Every name imported above is used by the snippet, so it compiles as-is under noUnusedLocals. The classes documented below that it does not branch on (AlterSDKError, GrantNotFoundError, GrantNotDelegableError, …) are deliberately not imported here — add them when you add a branch for them.

Class hierarchy

Base

• AlterSDKError — root of the hierarchy. Every other exception extends this.
• AlterValueError — input validation failed at the SDK boundary. Distinct from BackendError so callers can branch on “I passed something bad” vs “the backend said no.”

Backend errors

• BackendError — generic backend failure. details.status_code is populated when an HTTP status code is the proximate cause.
• RestrictedGrantRequiresProxyError — the grant is restricted to the proxy call path; use proxyRequest().
• SiblingLabelConflictError — the sibling label is already in use on this connection; pick another label.
• ReAuthRequiredError — the user must re-authorize via Alter Connect. Parent class of the grant-state errors below (GrantExpiredError, GrantRevokedError, GrantDeletedError, CredentialRevokedError), so one instanceof catch covers every “send the user back through Connect” condition.

Grant state

• GrantExpiredError — the grant’s TTL has elapsed. Exposes providerId, agentId, appUserId, populated only on the delegation-path expiry (a TTL-lapsed delegation chain); undefined on the root-path TTL expiry.
• GrantRevokedError
• GrantDeletedError
• GrantNotFoundError
• AgentDelegationMissingError — extends GrantNotFoundError (so an instanceof GrantNotFoundError catch still fires). Thrown on the agent path when request(method, url, { grantId }) / proxyRequest({ grantId }) hits a grant_not_found — the grant is not delegated to this agent, or a user/base grant id was passed where the agent’s own delegation id (listGrants) was required. Recover by delegating the agent through Connect, or resolve by provider (omit grantId). The App/operator path is unaffected.
• GrantNotDelegableError — extends BackendError. Thrown by agent.delegate() when the held grant is not delegable, or a managed secret’s operator ceiling blocks re-delegable grants (HTTP 403 grant_not_delegable).
• CredentialRevokedError

Identity resolution

• AmbiguousGrantError — multiple grants match the identity + provider tuple. Pass account or use direct grantId mode.
• NoDelegatedGrantError — the calling agent has no delegation for the resolved user on this provider. Recoverable via createConnectSessionForError().

Authorization

• PolicyViolationError — backend policy denial.
• StepUpRequiredError — extends PolicyViolationError. A content_match step-up obligation requires a fresher user session.
• RedactDischargeFailedError — extends PolicyViolationError. The request was denied because a redact obligation could not be applied safely.
• InsufficientScopeError — API key lacks the required scope.
• TokenRefreshInProgressError — concurrent refresh in flight; retry shortly.
• QuotaExceededError — a request-quota policy window is exhausted. Exposes retryAfter (seconds until the window resets, capped at 2,678,400 seconds / 31 days — a quota window is a calendar period up to a month long, and the response reports the longest exhausted one; may be undefined). A policy denial, not a transient outage — the SDK never auto-retries it.
• RateLimitError — the platform rate limit for the API key (or the organization-wide aggregate, when configured) is exhausted. A transient throttle, not a denial: wait retryAfter seconds and retry the same request (retryAfter is capped at 3,600 seconds — one hour, above the platform’s legitimate retry guidance). Also exposes scope (which ceiling was hit — a plain string, not a closed union, so a ceiling added later stays parseable; the known values are exported as RATE_LIMIT_SCOPE_VALUES, currently "ip", "api_key" and "organization", ordered outermost-first), limit, and windowSeconds. Each of those three may be undefined — not every response carrying this error code supplies them, so branch on a missing value rather than assuming one.

Provider

• ProviderAPIError — provider returned a 4xx/5xx that is not a scope or credential-rejection failure.
• ScopeReauthRequiredError — provider returned 403 insufficient_scope, or the backend already knew the grant’s scopes are drifted. Exposes missingScopes and providerId.
• ProviderUnauthorizedError — provider returned 401: the credential was revoked, expired, or otherwise invalidated provider-side. Exposes grantId, providerId, statusCode, responseBody. Recovery: re-authorize an OAuth grant via a new Connect session, or update the stored managed secret. A 401 whose WWW-Authenticate challenge carries error="insufficient_scope" (RFC 6750 — the credential is still valid, it just lacks a scope) surfaces as a generic ProviderAPIError instead.

Connect flow

• ConnectFlowError — generic flow failure, including an unavailable/expired token on the first poll, an unknown terminal state, or a total usage-limit application failure.
• ConnectDeniedError — user clicked Deny.
• ConnectConfigError — provider configuration issue (invalid redirect URI, unknown client, etc.).
• ConnectTimeoutError — Alter received no completion callback before the local deadline or before a session observed pending expired. details.reason is "poll_deadline_elapsed" or "session_expired"; without a callback, an exact provider-side error is unknowable.

Approvals

• ApprovalError — base class.
• ApprovalDeniedError
• ApprovalExpiredError
• ApprovalTimeoutError — local wait elapsed before any decision. Original transient (when present) is preserved on .cause.
• ApprovalExecutionFailedError

Managed agents

• AgentError — base class.
• InvalidKeyError
• KeyExpiredError
• KeyRotationExpiredError
• KeyInactiveError
• KeyAppNotFoundError
• AgentNotFoundError
• CallerAgentMismatchError
• CallerAgentResolutionError
• AgentNameExistsError
• AgentConcurrentUpdateError — the agent changed after it was read. Fetch it again, recompute the full desired scope allowlist, and retry with the fresh version.
• AgentInactiveError
• AgentRevokedError
• MeRequiresAgentKeyError — agent.me() was called through an impersonating Agent returned by App.getAgent(), so the request still used an application key rather than a genuine agent key.
• KeyRevokedError
• KeyAlreadyRevokedError
• KeyNotFoundError
• LastActiveKeyError — would revoke the agent’s only remaining active key. Pass force: true to override.
• AgentKeyLimitError — the mint would take the agent past its per-agent active-key cap. Revoke a key it no longer uses, then retry.
• AgentCannotMintSubagentsError
• IdempotencyKeyBodyMismatchError
• IdempotencyKeyAgentRevokedError
• IdempotencyKeyAgentInactiveError

Network

• NetworkError — TCP / DNS / socket failure.
• TimeoutError — extends NetworkError. Local or remote timeout.

Common fields

Every AlterSDKError carries details: Record<string, unknown>. toString() returns only the safe message and never stringifies details. Common detail keys:

Key	Type	Description
status_code	number	HTTP status code from the backend or provider.
grant_id	string	Grant the call resolved to (when applicable).
provider_id	string	Provider slug (when applicable).
method, url	string	HTTP method and pre-injection URL.
reason	string	Backend-reported reason code.
retry_after	number	Seconds to wait before retrying — a quota window reset or a rate-limit backoff. QuotaExceededError and RateLimitError also expose it as the typed retryAfter field (may be undefined). On both, the typed field prefers the Retry-After response header over this body value and caps the result — at 3,600 seconds for RateLimitError, at 2,678,400 (31 days) for QuotaExceededError, whose windows are calendar periods — so the two can differ.

Typed fields

The following public fields supplement message, name, and details:

Class	Fields
GrantExpiredError	providerId, agentId, appUserId (string | undefined)
GrantRevokedError	grantId: string | undefined
CredentialRevokedError	grantId, providerId, appUserId (string | undefined)
GrantNotFoundError	providerId, agentId, appUserId (string | undefined)
AmbiguousGrantError	providerId, accountIdentifiers, accountWasProvided, appUserIds, grantIds, candidates
NoDelegatedGrantError	providerId, agentId, appUserId (string | undefined)
PolicyViolationError	policyError: string | undefined
StepUpRequiredError	maxSessionAgeSeconds: number | undefined; inherited policyError is "step_up_required"
RedactDischargeFailedError	no extra fields; inherited policyError is "redact_discharge_failed"
SiblingLabelConflictError	label: string | null
InsufficientScopeError	required, granted, missing, scopeVersion, currentScopeVersion, scopeVersionMismatch, documentationUrl; aliases requiredScopes, grantedScopes, docsUrl
TokenRefreshInProgressError	grantId: string | undefined
QuotaExceededError	retryAfter: number | undefined
ProviderAPIError	statusCode: number | undefined, responseBody: string | undefined
ScopeReauthRequiredError	grantId, providerId, missingScopes; inherits provider response fields
ProviderUnauthorizedError	grantId, providerId; inherits provider response fields
ApprovalError and subclasses	approvalId: string | null
AgentError and subclasses	code: string, hint?: string

AmbiguousGrantError.candidates contains GrantCandidate entries with grantId, label, accountIdentifier, and accountDisplayName. The account fields are nullable.

For the typed exception fields and recovery flows for each code, see Errors.