API integration requirements: template and checklist

Short answer

An API integration requirements document is written so that both sides — the business and the technical team, or the company and the vendor — are sure they are building the same thing. A good document has twelve sections: purpose and scope, business scenarios, systems and owners, data, interfaces, authentication and security, volume and speed requirements, errors and retries, logging and audit, testing and acceptance criteria, rollout and rollback, and contacts and support. It does not have to be long — 6–10 pages is enough — but each section should record a decision, not a general intention.

Why integrations without a document drag on

Without a document, an integration often goes like this: the business says "leads should land in the CRM", a developer builds a webhook in a day, testing reveals the sales team also expected statuses to come back, and IT security asks where the keys are stored. Each new question adds a week, and in the end nobody can say when the project is "done", because no acceptance criteria were written.

A requirements document forces these questions before any code is written and closes them with both sides' sign-off.

Twelve sections

1. 11. Purpose and scopeWhy, what outcome is expected, and what is not part of this project.
2. 22. Business scenarios"A customer writes a number on WhatsApp → a lead is created in the CRM → assigned to a manager."
3. 33. Systems and ownersEach system, with its technical and business owner.
4. 44. DataObjects, fields, formats and a reference to the field map.
5. 55. InterfacesEndpoints, methods, events, sample request and response.
6. 66. Authentication and securityKey type, where it is stored, rotation, IP restrictions, permission scope.
7. 77. Volume and speedDaily request count, peak, expected response time, rate limits.
8. 88. Errors and retriesWhat each error means, when a retry happens, who is notified.
9. 99. Logging and auditWhat is logged, how long it is kept, who can view it.
10. 1010. Testing and acceptanceTest environment, test scenarios, "ready" criteria.
11. 1111. Rollout and rollbackPhases, cut-over date, how it is stopped if something goes wrong.
12. 1212. Contacts and supportWhom to write to, response time, on-call cover.

How to write a business scenario

A scenario is written step by step, without technical language, with "who" and "what" clear at every step. For each scenario write three variants: the normal case, an alternative case (the customer already exists in the CRM, say) and an error case (the CRM does not respond). The error case is the one most often forgotten — and the one that later causes the most trouble.

The interface section: samples matter

Naming the endpoint is not enough. For each interface add a real (anonymised) sample request and response: which fields are sent, which are required, what format the response has, what an error looks like. A document without samples leads two teams to understand the same word differently. Keep the field map itself in a separate document — its format is shown in the CRM integration data mapping checklist.

The security section

• Key or token: where it is stored (not in code), who can see it, how often it is rotated.
• Least privilege: the integration user can access only the objects and operations it needs.
• Network: IP restrictions, HTTPS only.
• Personal data: which fields are transmitted and why they are needed; anything unnecessary is not sent.
• If an AI calls a tool: which URLs it may reach and what it may change.

Volume, speed and limits

Write down the daily request count, the peak hour and the increase on campaign days. Write down the other side's API limits too: how many requests a minute it accepts, and what happens when that is exceeded. Without this section the integration works in testing and then hits the limit on the first campaign day, with leads stuck in a queue.

Testing and acceptance

1. 1Test environmentNo live data, but the real structure.
2. 2Scenario listThe normal, alternative and error variant of each business scenario.
3. 3Acceptance criteriaMeasurable: time, result, behaviour in an error case.
4. 4Sign-offThe business owner and the technical owner approve acceptance in writing.

A filled-in example: one scenario

This is an illustrative example. Scenario: "A customer asks about order status in chat." Normal case: the AI asks for the order number, calls the order system's read endpoint and tells the customer the status. Alternative case: the number is not found — the AI asks the customer to check it, and on a second failure hands over to an agent. Error case: the API does not respond within 5 seconds — the AI tells the customer it cannot check the status right now and a notification goes to an agent. Acceptance criterion: the expected behaviour on all 20 requests in the test environment.

Common mistakes

• Writing only the "happy path" — no error cases.
• No acceptance criteria — the project never "finishes".
• Leaving key storage for later.
• Not writing down volume and limits.
• Writing the document once and not recording changes.

Limitations

A requirements document does not prevent every surprise: the other side's API may change, and unexpected data formats may arrive. So the document must be kept alive and changes recorded with dates. Requirements for transferring personal data and for security must be checked separately against the company's own policy and local law.

Integrating with Vexvon

When integrating with Vexvon, a company offers its own API to the AI as a tool and writes when it should be called — for example, "when the customer asks about order status"; tool calls are protected against SSRF. In the other direction, events such as a new lead, a completed call and a status change are sent to the company's system by webhook. Channels connect through official APIs without sharing passwords. For large companies we fill in the security questionnaire and sign an NDA. More on integrations and security.

Next step

Open the twelve sections as a blank template and fill in the first two — purpose and scenarios — with the business owner. The technical team will derive the rest from those two. For the overall concept, see enterprise AI integration; for chatbot architecture, see chatbot API and webhook integration. More articles are in the enterprise integration section, and we can review your document together during a demo.