Integration spec · data mapping, auth, reliability, webhooks, testing
Scope an API integration before it scopes you.
A fill-in requirements template for any API integration: the business goal, the exact data mapping, authentication, error and retry handling, rate limits, webhooks, and a test plan. Most integration disasters trace back to a question nobody asked up front. This template asks them, so the build ships without ugly surprises.
Why integrations go sideways
An API integration looks simple in the demo and gets complicated in production. The provider rate-limits you mid-sync, a field arrives null that the docs swore was required, a retry creates a duplicate charge, a webhook gets delivered twice and out of order. None of these are exotic — they are the normal behavior of networked systems. The teams that ship clean integrations are the ones that decided how to handle all of it before writing the first line.
This template captures those decisions. It is the same scoping we do on every API and integration project we take on. If you want the underlying concepts, the API, webhooks, and idempotency glossary entries are quick primers on the terms used throughout.
1. Business objectives & scope
- Business objective: state in one sentence what this integration must achieve and how you will know it worked.
- Direction of data: define whether you are reading, writing, or both, and which system is the source of truth for each entity.
- Sync model: real-time, scheduled batch, or event-driven — and the freshness the business actually requires.
- Scope and non-goals: list what is explicitly in and out, so the build does not quietly expand.
- Volume: estimate request and record volumes today and at expected growth, since they shape every other decision.
2. Data mapping & contracts
- Field mapping: for every field you read or write, record the source field, the destination field, the type, and its meaning.
- Identifiers: define how records are matched across systems and how you handle differing ID formats.
- Transformations: document any conversions — units, currencies, timezones, enumerations — and where they happen.
- Edge values: decide how you handle nulls, missing fields, truncation, and unexpected types rather than discovering them in production.
- Schema versioning: note how you will detect and absorb changes to the provider's data contract over time.
3. Authentication & security
- Auth mechanism: capture how the API authenticates — OAuth 2.0, API keys, signed requests — and the scopes you need.
- Credential handling: store secrets in a secrets manager, scope them to least privilege, and define how they rotate.
- Environments: separate credentials and endpoints for sandbox and production so a test can never touch live data.
- Transport security: require HTTPS, and verify certificates and webhook signatures where applicable.
- Access boundaries: record exactly what data the integration can reach and confirm it is no more than needed.
4. Error handling & reliability
- Failure modes: list how the API can fail — timeouts, 4xx, 5xx, rate limits — and the intended response to each.
- Retries and backoff: define a retry policy with exponential backoff and a cap, and which operations are safe to retry.
- Idempotency: make write operations idempotent so a retry cannot create duplicates.
- Dead-letter and alerting: decide where a permanently failing message goes and how a human is told about it.
- Degradation: define what your product does when the integration is down, rather than failing the whole flow.
5. Rate limits & performance
- Rate limits: record the provider's documented limits and design your call patterns to stay safely under them.
- Throughput targets: state the latency and volume your integration must support, and how you will measure it.
- Batching and caching: decide where you batch requests or cache responses to reduce load and cost.
- Quotas and cost: note any usage-based pricing so the integration's cost is understood before launch.
6. Webhooks & events
- Webhooks: list the events you will receive, and verify each payload's signature before trusting it.
- Delivery guarantees: account for duplicate and out-of-order delivery, and process events idempotently.
- Reconciliation: define a periodic sync to catch anything a missed webhook left inconsistent.
- Replay: decide how you handle replayed or backfilled events without corrupting state.
7. Testing & rollout
- Test environment: confirm a sandbox exists, and define the scenarios — success, failure, rate limit, malformed data — you will exercise.
- Acceptance criteria: write the conditions that must be true for the integration to be considered done.
- Monitoring: define the metrics and alerts that tell you the integration is healthy in production.
- Rollout: plan a staged release with a rollback path, and a runbook for the on-call engineer.
How to use this template
Fill in the objectives, data, and reliability sections before you commit to a specific provider — your requirements should drive the choice, not the reverse. Once a provider is selected, complete the authentication, rate-limit, and webhook sections against their actual documentation, not your assumptions. The data mapping section is the one to take most seriously: most integration bugs are data bugs, and mapping every field with its type and meaning kills a whole class of them up front.
Treat the finished document as the contract between everyone involved — product, engineering, and the vendor. It becomes your test plan and your acceptance criteria. If the integration handles money, pair it with our Stripe integration checklist, which applies this same error-handling and webhook discipline to a payments API specifically.
How this connects to our work
Disciplined scoping is how we approach every API development engagement, whether we are consuming a third-party API or building one for others to consume. The same reliability thinking shows up in our Stripe integration work, where idempotent writes and verified webhooks are non-negotiable, and in our SaaS platform development, where integrations are often the connective tissue of the product.
If you are planning a tricky integration and want a second opinion on the requirements, or you have one that keeps dropping data and needs a rethink, see how we scope and price the work or reach out to talk it through.
Frequently asked questions
When should we fill this out — before or after picking the API?
Fill in the goals, data, and reliability sections before you commit to a specific third-party API. Requirements should drive the choice of provider, not the other way around. Once a provider is chosen, complete the auth, rate-limit, and webhook sections against that provider's actual documentation.
Why does data mapping deserve its own section?
Because most integration pain is data pain. Mismatched field types, different ID formats, unexpected nulls, and timezone or currency assumptions surface late and cause silent corruption. Mapping every field you read and write up front, with its type and meaning, is the cheapest way to avoid a class of bugs that are miserable to debug in production.
Do we really need to plan for errors and retries before building?
Yes. Third-party APIs fail, rate-limit, and time out — that is normal operation, not an edge case. Deciding up front how you retry, where you make operations idempotent, and how you surface a persistent failure to a human is the difference between an integration that heals itself and one that quietly drops data.
Is this template only for third-party APIs?
It is written with third-party integrations in mind, but it works just as well for an internal service you depend on. The same questions — contract, auth, failure modes, rate limits, and testing — apply whether the API belongs to a vendor or another team in your own company.
Related resources & reading
API Design Guidelines Checklist
The conventions to follow if you are building the API too.
Stripe Integration Checklist
The same discipline applied to a payments integration.
Next.js Stripe Integration Guide
Error handling and webhook verification in a real build.
API Development
How we design, build, and integrate APIs end to end.
Planning a tricky integration?
Whether you are scoping a new integration or untangling one that keeps dropping data, we can help you nail the requirements and build something reliable. See how engagements are priced or book a call.