API and data glossary

39 terms you meet when you call a public-data API, each with a plain definition and how Onekey handles it. Every entry links to the docs page that covers it.

A

API keyA secret string that identifies the caller and is sent with every request.

B

Batch requestMany calls sent together in one HTTP request.

C

Cache hitAn answer served from stored data instead of fetched fresh.Canonical schemaOne fixed set of field names and types that every source is mapped onto.Computed blockValues derived by the API from the fields it returns, kept apart from the source data.Constant-time comparisonComparing two secrets in a way whose duration does not reveal how much matched.CreditThe unit an API bills in; each call costs a published number of them.Cursor paginationPaging through a list by sending back a token from the previous page instead of a page number.

D

DeltaA description of what changed between two versions of the same data.

E

Exponential backoffWaiting longer after each failed attempt, usually doubling the wait.ext fieldA platform-specific value kept outside the shared schema.

F

Fan-outSending one query to several sources at once and collecting the answers.Freshness (age_s)How old the data in a response is.

H

HMACA keyed hash that proves a message is unaltered and came from someone holding the key.Honest nullReturning null for a value that is unknown instead of a made-up zero, false or empty string.

I

Idempotency keyA unique value you send with a request so that repeating it is safe.Idempotent replayA stored answer returned again for a repeated idempotency key.

J

JitterA small random amount added to a wait so many clients do not retry in step.

L

llms.txtA plain-text file that maps a site’s documentation for language models.

M

MCP (Model Context Protocol)An open protocol that lets AI assistants call tools and read data from other services.

N

Negative cachingRemembering that something does not exist, so the question is not asked again.

O

OpenAPIA machine-readable description of an HTTP API’s routes, parameters and responses.

P

Page sizeHow many results one page of a list holds.Partial successA request that ran several parts, where some worked and some did not.Per-key credit limitA spending cap set on one API key, separate from the account balance.

R

Rate limitA cap on how many requests a caller may make in a period.Reciprocal rank fusion (RRF)A way to merge ranked lists by adding 1/(k + rank) for each list an item appears in.Refund (failed call)Giving credits back when a call does not deliver an answer.Replay windowHow old a signed message may be before it is refused.Request IDA unique identifier for one request, used to trace it.Response envelopeThe fixed outer shape every response has, wrapping the data.Retry-AfterA response header saying how many seconds to wait before trying again.

S

Server-Sent Events (SSE)A one-way HTTP stream where the server pushes named events as they happen.SSRFTricking a server into making requests to addresses it should not reach.Stable and betaWhether an endpoint has been verified against the live source.Stale responseA cached answer older than its fresh window, served now while it refreshes.

U

URL lookupResolving a public link to the endpoint that serves it.

W

WebhookAn HTTP request the service sends to your URL when something happens.Webhook signatureA value that proves a webhook came from the sender and was not altered.