Building a Unified API: A Detailed Implementation Checklist

On this page

1. 1. Scope
2. 2. The common model
3. 3. Adapters
4. 4. Raw data
5. 5. Authorization
6. 6. Sync (if you store data)
7. 7. Testing
8. 8. Observability
9. 9. Documentation
10. 10. Maintenance
11. Common pitfalls
12. Where Pathfix fits
13. Frequently asked questions

This is a working checklist for teams building their own unified API layer, typically one internal interface that covers several providers in a category, such as CRMs, calendars or accounting systems. It assumes you've already decided a unified layer is right for your product. If you haven't, start with Unified APIs Explained.

1. Scope#

• List the exact product features the unified layer must support.
• List the providers needed for launch, and those likely in the next year.
• For each feature, list the operations: read, create, update, delete, search.
• Decide whether the layer must support writes at launch. Reads are far simpler.
• Decide on real-time calls versus synced storage.

Keep the scope tied to what your product uses. A general-purpose model is a product in itself.

2. The common model#

• Define each entity your product needs, such as contact, company or event.
• For each field, document its meaning, type, whether it's required, and which providers support it.
• Use stable internal IDs and keep each provider's native ID alongside them.
• Decide how to represent fields that only some providers have: optional fields, an extension object, or both.
• Define how you'll represent enumerations such as stages or statuses that differ between providers.
• Version the model so changes don't break consumers.

3. Adapters#

For each provider:

• Map every model field to the provider's field, with transformation rules.
• Document fields that can't be mapped.
• Handle pagination in the provider's style: cursors, pages or offsets.
• Handle filtering and incremental fetches, such as modified-since queries.
• Translate provider errors into a common error set.
• Respect provider rate limits and back off on 429 responses.
• For writes, validate against the provider's required fields before sending.

Keep adapters isolated so a change for one provider can't affect another.

4. Raw data#

• Store or log the raw provider response alongside normalized output, subject to your data policies.
• Use raw data to backfill new model fields without re-fetching everything.
• Use raw data to debug mapping issues.

5. Authorization#

• Register OAuth apps for each provider and plan for app review where needed.
• Store tokens securely and associate each connection with a tenant and user.
• Handle refresh, rotation and revocation per provider.
• Record granted scopes and check them before operations that need specific permissions.
• Provide a reconnect flow when access breaks.

6. Sync (if you store data)#

• Initial backfill with progress tracking and resumability.
• Incremental sync using webhooks where available, plus scheduled reconciliation.
• Deletion handling, including soft deletes and merged records.
• Conflict rules if data flows in both directions.
• Per-tenant isolation in storage and processing.

7. Testing#

• Fixture tests for each adapter using recorded provider responses.
• Scheduled tests against provider sandboxes to catch API changes.
• Tests for edge cases: empty fields, unicode, very large records, deleted records, permission errors.
• Contract tests for the common model.

8. Observability#

• Metrics per provider: request volume, error rates, latency, rate-limit hits.
• Per-tenant logs of sync runs and failures, without sensitive data.
• Alerts for sudden error increases on a single provider.
• A way for support to see a customer's connection status.

9. Documentation#

• Internal docs for the model, including per-provider support for each field.
• A changelog for model versions.
• Notes on each provider's quirks and limits.

10. Maintenance#

• An owner for each adapter.
• Subscriptions to provider developer announcements and deprecation notices.
• A schedule for reviewing API version upgrades.
• A process for adding a field to the model.

Common pitfalls#

• Modelling everything up front. Start with what your product needs and grow.
• Dropping unmapped data. You'll need it later.
• Treating writes like reads. Each provider validates differently.
• Ignoring per-provider rate limits during backfills.
• Assuming enumerations line up. Pipeline stages, statuses and categories rarely match across providers.

Where Pathfix fits#

Section 5 is the same work for every provider. Pathfix OAuth handles authorization, token storage, refresh and authenticated API passthrough across 350+ providers, using your own OAuth apps. Your adapters call each provider's own API through Pathfix, and your team keeps full control of the model and mapping. Pathfix isn't a unified API itself.

See supported providers and the documentation.

Frequently asked questions#

How many providers justify a unified layer?#

There's no fixed number, but the benefit grows once you have three or more similar providers serving the same feature.

Should the model mirror the most popular provider?#

It's tempting, but it makes other adapters awkward. Model your product's needs instead.

Real-time or synced?#

Real-time is simpler and fresher but bound by provider latency and rate limits. Synced storage is faster to query but needs sync infrastructure and raises data residency questions.