LOCKEDIN / FORWARD-DEPLOYED ENGINEERING 101
Understand it.
Then build it.
You can be an experienced engineer and still be new to agents. Start with what each thing is and how it helps a person do useful work. Explore 58 original introductions across software, agents, cloud, security and delivery. Start here without a model key; each topic connects to deeper instruction and practice.
A place to start.
Choose a short reading route, or look up a concept below.
- 101UnderstandPlain language, visual walkthrough, vocabulary
- 102Build with guidanceOriginal lessons, examples and knowledge checks
- 103Practise and explainRunnable labs, failure cases and handover
Connect the software
Move from a person using a command to one program requesting something from another.
See the 9-concept route
For people who want the software vocabulary behind AI tools, or a refresher before their first local build.
- 01Terminal & CLIBegin with a person issuing a command to a program; the terminal is not itself an agent.
- 02ConfigurationUnderstand how that program receives its settings and why different processes can behave differently.
- 03JSON & schemasRead the messages programs exchange. Separate a field's name, type and meaning before following an API request.
- 04APIsYou are here
- 05RESTSee how resource addresses, HTTP methods and status codes organize a web API.
- 06SDKsFollow the library code that turns a convenient method call into an API request.
- 07TestsDecide what observable behavior to check before trusting a change made by a person or an agent.
- 08GitSeparate editable files, selected snapshots and recorded commits. Match the tested content to the change you hand over.
- 09Claude CodeBring commands, configuration and checks into a bounded coding-assistant task.
Bookmark this page to return to this concept. The number shows your place in the reading route; it is not an assessment result.
A software contract
What is an API?
An application programming interface (API) is an agreed way for one piece of software to use another. It specifies operations, inputs, outputs and errors. Some APIs are local functions; a web API exchanges requests and responses across a network.
An agent becomes useful through connections to business systems. Those connections need clear contracts and failure behavior.
UNDERSTAND THE SYSTEM
An API is the agreed doorway into a system
An application programming interface (API) defines how software asks another component to do something. It specifies inputs, outputs and errors; it may be local code or a network service.
Read the connections in plain English
- 01Calling application → API contract
The caller follows the agreed interface.
- 02API contract → Service checks
A well-shaped request still needs authorization.
- 03Service checks → Order store
Access is limited to records the caller may read.
- 04Order store → Response
The service formats the permitted result; the caller does not connect directly to the store.
Check your understanding: Is an API the same as a database?
No. An API is an interface. The service behind it might use a database, another API or a calculation. Callers should rely on the interface contract, not hidden storage details.
CONNECT IT TO WHAT YOU KNOW
Start with something familiar.
It is like a typed function boundary between teams. You can ask for an operation without knowing the implementation behind it.
An API is an interface. A model can suggest an API call; your application must validate it, authorize it and actually execute it.
Words worth knowing
- Client
- The software making a request.
- Server
- The software handling it.
- Endpoint
- A network address and operation exposed by a service.
Useful foundations
Open a definition and diagram here. Your lesson stays in place.
Data a program can read and checkWhat are JSON and schemas?
QUICK REFERENCE / 101
What are JSON and schemas?
JSON (JavaScript Object Notation) is a text format for exchanging data between programs. An object pairs field names with values, like a small form with named boxes. JSON Schema describes rules for those values. Neither is an AI model, and JSON works with many programming languages.
An API response, an agent's tool arguments and a model's structured answer often arrive as JSON. Before connecting them, an FDE needs to read the fields, recognize their types and explain why readable data can still be wrong for the task.
ONE EXAMPLE / FICTIONAL CASE
Follow the connections.
A maintenance assistant asks a service for the status of ticket T-104. It should receive only fields its caller may read.
UNDERSTAND THE SYSTEM
An API is the agreed doorway into a system
An application programming interface (API) defines how software asks another component to do something. It specifies inputs, outputs and errors; it may be local code or a network service.
See what moves and why.
Read the connections in plain English
- 01Calling application → API contract
The caller follows the agreed interface.
- 02API contract → Service checks
A well-shaped request still needs authorization.
- 03Service checks → Order store
Access is limited to records the caller may read.
- 04Order store → Response
The service formats the permitted result; the caller does not connect directly to the store.
Check your understanding: Is an API the same as a database?
No. An API is an interface. The service behind it might use a database, another API or a calculation. Callers should rely on the interface contract, not hidden storage details.
Work through it, step by step.
Request
The client supplies the operation, ticket identifier and authentication material through the documented interface.
What you have now: A request for T-104
Check and execute
The server checks identity, access and input before reading the ticket. A valid identifier alone is not permission.
What you have now: An authorized lookup
Respond
The server returns a status and a documented result or error. The client handles a missing ticket and a timeout differently.
What you have now: An outcome the client can interpret
Follow one API request
Original silent explainer · Optional English captions
Read the visual transcript
- Request: a client asks for ticket T-104 through an agreed interface.
- Check: the server validates the input and authorizes this caller before accessing the record.
- Response: the server returns a documented result or error. A timeout means the result may be unknown.
FROM RECOGNITION TO REASONING
Write a tiny ticket lookup contract on paper.
- 01
Specify one allowed input and three returned fields.
- 02
Describe missing, unauthorized and unavailable outcomes.
- 03
State which fields an agent must never be allowed to choose, such as its own tenant identity.
A request/response example and three error cases, using invented identifiers.
Compare your reasoning when you are ready
A well-formed request can still be unauthorized. The server derives authority from trusted identity, while the model may supply a proposed ticket identifier.
Keep notes in your own working copy. Moving through these cards does not record completion.
TURN THE IDEA INTO USEFUL WORK
You can now go deeper.
An API is an interface. A model can suggest an API call; your application must validate it, authorize it and actually execute it.
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