How to plan an API project that lasts.
Design, security, documentation and AI readiness: the decisions that separate an API your team relies on from one it works around.
An API is the contract between your systems: your website, your mobile app, your CRM, your accounting software and, increasingly, AI assistants. When it is planned well, new features plug in quickly. When it isn’t, every change becomes a project. If you are new to the topic, start with what an API is and when your business needs one. This guide covers how to plan one.
Step 1: Start with who will use it
Every good API design begins with its consumers, not its database. List them before anything else:
- Your own front ends: the website, the iOS and Android apps, an admin dashboard.
- Internal systems: ERP, CRM, accounting, scheduling, inventory.
- Partners and customers: dealers, vendors or clients who need a data feed.
- AI tools: assistants and agents that look up data or take actions on a user’s behalf.
For each one, write down what it needs to read, what it needs to change, and how fresh the data must be. That list becomes your first set of endpoints and permissions.
Step 2: Pick the right style
| Style | Best for | Trade-off |
|---|---|---|
| REST | Most business integrations and partner APIs | Several calls may be needed for complex screens |
| GraphQL | Apps with many screens pulling related data | Caching and access control take more care |
| Webhooks | Telling other systems the moment something happens | Receivers must handle retries and duplicates |
| Real-time (WebSockets) | Live tracking, chat, dashboards | More infrastructure to run and monitor |
| gRPC | High-volume service-to-service calls | Less friendly for browsers and partners |
Most business projects use REST as the backbone with webhooks for events. Mixing styles is normal; the key is choosing per use case, not per trend.
Step 3: Design the contract first
Before writing code, describe the API in an OpenAPI specification (or a GraphQL schema). That document defines every endpoint, field, error and permission. It lets front-end and back-end work happen in parallel, generates documentation automatically, and makes review easy for non-developers.
- Use consistent, plain names:
/customers/{id}/orders, not/getCustOrd. - Return predictable errors with clear messages and codes.
- Paginate lists from day one so growth doesn’t break clients.
- Version the API (
/v1/) so you can improve it without breaking existing apps. - Make write operations safe to retry, so a dropped connection never creates a duplicate order.
Step 4: Build security in, not on
The OWASP API Security Top 10 is the standard checklist, and broken authorization tops it for a reason: most API breaches come from an API returning data the caller should never see.
- Authentication: OAuth 2.0 or OpenID Connect for users; scoped, rotatable keys for systems.
- Authorization on every object: check that this user can see this record, not just that they are logged in.
- Least privilege: partners and AI tools get only the scopes they need.
- Rate limiting: protects against abuse and runaway scripts.
- Validation and logging: reject bad input early and keep an audit trail of who changed what.
Step 5: Make it ready for AI
AI assistants are becoming another client of your API. Tools built on models like Claude and OpenAI’s call APIs to look things up and take actions, and the open Model Context Protocol (MCP) gives them a standard way to discover what your system can do. An AI-ready API has:
- Clear descriptions on every endpoint and field, because the model reads them to decide what to call.
- Small, well-named actions (“create quote”, “check order status”) instead of one giant endpoint.
- Separate, narrowly scoped credentials for AI tools, with human confirmation for anything irreversible.
- Logging that shows exactly what an agent did and on whose behalf.
Step 6: Plan for life after launch
- Documentation: generated from the spec, with examples, kept current automatically.
- Monitoring: uptime, error rates and slow endpoints, with alerts.
- Testing: automated contract tests so a change never silently breaks an app.
- Deprecation policy: how long old versions keep working, and how clients are told.
A quick planning checklist
- List every consumer and what it reads and writes.
- Choose the style for each use case.
- Write the OpenAPI or GraphQL contract and review it.
- Define authentication, scopes and rate limits.
- Decide how AI tools will connect, if at all.
- Set up docs, monitoring and automated tests before launch.
How we help
We design and build APIs that connect websites, mobile apps and business software, including integrations with ERPs, CRMs, payment systems and AI models. See our API development and custom software development services, or read our guide to website and mobile app architecture to see where the API fits in the bigger picture.
Frequently asked questions
Should I use REST or GraphQL?
REST suits most business integrations and partner APIs. GraphQL helps when apps have many screens pulling related data and you want to reduce round trips. Many systems use REST for partners and GraphQL for their own apps.
What is an OpenAPI specification?
It is a standard, machine-readable description of an API: its endpoints, fields, errors and authentication. It drives documentation, testing and code generation, and lets teams agree on the API before building it.
How do I make my API work with AI assistants?
Give endpoints clear descriptions, keep actions small and well named, issue narrowly scoped credentials for AI tools, require confirmation for irreversible actions, and consider exposing it through the Model Context Protocol (MCP).
What is the most common API security mistake?
Broken object-level authorization: checking that a user is logged in but not that they are allowed to see the specific record they requested. It tops the OWASP API Security Top 10.