API Performance Optimisation
When an API is slow, every app, partner integration and internal service calling it inherits the delay. GullySystem measures response times endpoint by endpoint and fixes what is making specific calls slow.
Why a Slow API Is Everyone's Problem at Once
A slow screen affects the people looking at that screen. A slow API affects every mobile app, partner system and internal service that calls it, often at the same time, which is why a single endpoint left unoptimised can quietly slow down several products you did not think were connected.
Where API Latency Usually Comes From
Serial Calls That Could Run Together
An endpoint waiting for three separate lookups one after another, when those lookups do not depend on each other and could run at once.
Oversized Responses
Sending an entire record or a full list when the caller only needed a few fields, which costs time on both ends of the connection.
No Rate or Load Awareness
One caller with a runaway retry loop or a crawler hitting an endpoint far more often than a person would, slowing the response for every legitimate caller sharing it.
Authentication and Middleware Overhead
Checks that run on every request — token validation, logging, permission lookups — adding up when they are not written efficiently.
What We Measure Before Changing Anything
- Response time for each endpoint, separated from the time spent by the caller's own network
- How response time changes as the number of concurrent calls rises
- Which endpoints are called most often and which are called least but cost the most per call
- Error and timeout rates under normal and peak conditions
Fixes We Commonly Apply
Parallelising Independent Work
Lookups that do not depend on each other's result are made to run together instead of in sequence.
Response Shaping
Endpoints are changed to return only the fields a caller actually uses, with pagination for anything returning a large list.
Rate Limiting and Throttling
Limits are set so one heavy caller cannot degrade the response for every other integration sharing the same endpoint.
Versioned Changes
Where a fix changes what an endpoint returns, it is released as a new version so existing integrations keep working while new callers move to the improved response.
Who Depends on This Working
Companies With a Public or Partner API
Where slow responses affect other businesses integrating with you, not just your own team.
Mobile App Backends
Where every screen in the app waits on an API call, and a slow endpoint is felt as a slow app even though the app itself is fine.
Internal Microservices
Where one slow service quietly becomes the bottleneck for every other service that calls it.
Frequently asked questions
Is this the right service if our app is slow but the API itself responds quickly?
No — if the API itself measures fast and the delay is inside the app's own screens, that points to frontend or backend application work instead. This service applies specifically when the endpoints themselves are what is slow, which is worth confirming with measurement before committing to either.
How do you measure API performance without disrupting live traffic?
By timing real calls that are already happening wherever possible, and by running additional test calls at controlled volume against a staging copy for anything that needs load beyond normal traffic. Production monitoring for this is read-only and does not interfere with real requests.
Can you fix an API without breaking apps or partners already using it?
Yes. Where a fix would change the shape of a response, it is released as a new version so existing callers keep receiving what they expect while new or updated integrations move to the faster version on their own timeline.
What determines the cost of this work?
The number of endpoints in scope, how many depend on external services outside our control, and whether the cause is isolated to specific endpoints or spread across shared code such as authentication that every request passes through.
Do you work with REST, GraphQL, or both?
Both. The measurement approach differs slightly — a GraphQL query can request very different amounts of data through the same endpoint — but the underlying causes of slowness and the fixes for them are largely the same.
Will you need access to third-party services our API calls?
Where your API is slow because it is waiting on a third-party service, we need enough visibility to confirm that is the cause, though we cannot change a third party's own performance — only how your API waits for, caches or works around it.
What do you need from us to start?
API documentation or a way to explore the endpoints, access to server-side logs or monitoring if any exists, and a list of which integrations or apps are the priority so testing reflects how the API is actually used. Every change lands directly in your own codebase, so nothing about running the API afterwards depends on us.
Tell us what you need.
Send a short brief and one of our engineers will come back to you — usually the same day.
- No obligation
- We reply the same working day
- Your details stay private