ballerina

name

ballerina

description

Writes, runs, and tests Ballerina programs and integrations. Use when the user asks to write, create, implement, update, or fix Ballerina code; create or set up a new Ballerina project or package; build an HTTP service, API, or integration in Ballerina; run, test, or build a Ballerina project; add a library or dependency; or when the user does not have Ballerina installed and needs help setting it up.

Creating a New Project

When the user asks to create a new project, service, or program from scratch:

bal new <project-name>   # scaffolds main.bal + Ballerina.toml
cd <project-name>

• Read the generated Ballerina.toml to understand the package (name, org, version)
• For a workspace (multiple packages in one repo), see workspace rules in code-rules.md

Writing Ballerina Code

Step 1 — Read existing code and plan file layout: Read .bal files and Ballerina.toml to understand the project and its existing layout. Place new code in the file that fits its concern rather than everything in main.bal (see code-rules.md for file organization).

Step 2 — Discover libraries if needed: If the task needs an external connector or library you don't know, invoke the library agent — give it the full task (including auth and trigger/event details) so its first summary already covers the client or listener constructor and the auth/connection config you'll need. Add the returned import to your .bal file; bal build resolves the dependency from Central. Trust the summary's API shapes — don't bal pull or read package source to double-check them (that only adds latency); if a detail is genuinely missing, ask the library agent rather than guessing. Trusting it doesn't mean importing every package it names — import only what your code actually references.

• Need several libraries? Invoke the library agent for each in parallel (multiple agent calls in one step, or run them in the background) — the lookups are independent. Meanwhile keep doing other independent work (scaffold the project, read existing .bal files, plan the file layout), and fold in each summary as it returns. Don't block on one lookup before starting the next.
• When both a ballerinax/* connector (with its own listener) and a standalone trigger.* package cover the same events, always prefer the connector — trigger.* packages are being superseded (don't judge by modified date).
• No library agent (non–Claude Code agents)? Use bal directly: bal search <keyword>, then bal pull <org/name> and read its client.bal/types.bal under ~/.ballerina/repositories/central.ballerina.io/bala/<org>/<name>/<version>/any/modules/<name>/.
• Never hand-edit Dependencies.toml to add dependencies — it is auto-managed by the build tool. (Deleting it to force a clean re-resolution is fine.)
• Never edit Ballerina.toml to add dependencies — imports + bal build handle this automatically.

Step 3 — Write the code: Strictly follow the rules in code-rules.md — check your code against them as you write. If the Ballerina language server (LSP) is available, use the LSP tool to check the code as you write — hover to confirm a symbol's type/signature, goToDefinition/goToImplementation to inspect an API's real shape, findReferences/documentSymbol/workspaceSymbol to locate declarations (it does navigation/intelligence, not error diagnostics — bal build in Step 4 is the error check). Key rules:

• Use records for all data — never json or map<json> directly
• Two-word camelCase for every identifier
• Named arguments for every function/method call

Step 4 — Validate: Run bal build. Fix every error before moving on. Repeat until clean. If an error is about a library's own API (wrong method, listener, or service signature), re-consult the library agent's API summary — or ask it for the specific detail you're missing — rather than re-guessing. If errors remain after several attempts, stop and report each unresolved error with its file and line number.

For langlib API quick reference: langlib-reference.md

Running and Testing

• Test request → bal test; otherwise → bal run
• Always run bal build first — if errors, stop and report each one with file and line number
• On run: show full output; stop any started service when done
• On test: state what is being tested, show pass/fail count, fix failures and re-run

Ballerina Not Installed

If a bal command fails because Ballerina is not installed, read setup.md for installation instructions.

Errors and Unexpected Behavior

When bal build reports an error, a program panics at runtime, or behavior is unexpected, read troubleshooting/index.md to find the matching topic file. Do not preload every troubleshooting file — the index is a router that points to the one relevant file for the symptom.