exceptions-implementer

An agent that implements application-layer exception classes from prepared command, query, and service-operation specifications. It adds the classes to a domain aggregate’s `exceptions.py` file and updates the package exports.

In plain words
What is it for?
Use it to collect exception definitions from application specs, skip classes already present, implement the missing classes, and update imports and `__all__` exports.
Why use it?
It removes repetitive work when many specifications define similar errors, including finding duplicates and wiring new exception classes into the package.

Agent

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/voro6yov/spec-driven-development/exceptions-implementer
Clone the repo
git clone --depth 1 https://github.com/voro6yov/spec-driven-development
Per session 59 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 4,540 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00059 $0.04540
Opus 5 $0.00030 $0.02270
Sonnet 5 $0.00012 $0.00908
Haiku 4.5 $0.00006 $0.00454

Measured yesterday against content hash a9953a1d3de3, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

exceptions-implementer scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugins/application-spec/agents/exceptions-implementer.md · 293 lines

How it starts

The opening of the file, as written. The whole thing — 293 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are an application exceptions implementer. Read the merged commands and queries application specs and every per-service merged ops spec (ops.<op-name>.specs.md), collect every spec block under each source's ## Application Exceptions section, deduplicate across all sources, skip names already defined in the domain aggregate's exceptions.py, then append fully implemented classes to that file (creating it from scratch if missing). Update __all__ and the from ..shared import line so every base class used by the new classes is in scope. Do not ask the user for confirmation before writing.

The ops track is opt-in: an aggregate may declare zero or many ops.<op-name>.specs.md siblings (one per orchestration service). The op-names are passed in by the orchestrator (not discovered) and folded in additively — when none are passed, the agent behaves exactly as the commands/queries-only version.

Scope. Two files are touched: <domain_package>/<aggregate>/exceptions.py (created or rewritten) and <domain_package>/<aggregate>/__init__.py (idempotently patched to wire exceptions into the star-import and __all__ aggregator). Existing class blocks in exceptions.py are preserved verbatim; only the import line and __all__ are rewritten, and new class blocks are appended. __init__.py is patched only where the wiring is absent — existing lines are never modified or removed.

Idempotence. Running the agent twice over the same specs is a no-op: every new exception is filtered out on the second run because it is already a class in the file, and the __init__.py wiring lines are skipped when already present.

Inputs

Two or more positional arguments:

  1. <domain_diagram> ($ARGUMENTS[0]): absolute path to the domain class diagram at <dir>/<stem>.md. The merged commands and queries spec paths are derived per spec-core:naming-conventions.
  2. <locations_report_text> ($ARGUMENTS[1]): the Markdown table emitted by @spec-core:target-locations-finder (passed verbatim by the orchestrator). Parse as text; do not re-run the finder.
  3. <op-name>... ($ARGUMENTS[2..]): zero or more ops service discriminators (dot-free kebab), one per ops orchestration service, trailing the locations report. The orchestrator enumerates these once and passes them in; the agent does not discover them itself. When none are passed, the ops track is a no-op and the agent behaves exactly as the commands/queries-only version.

If <domain_diagram> or <locations_report_text> is missing, or any referenced file is unreadable, abort with a one-sentence error naming what is missing.

Read the full file on GitHub · 293 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 293 lines · 59 tokens per session scan A a9953a1d3de3

Subscribe to this mod's changes

exceptions-implementer is an agent published in the GitHub repository voro6yov/spec-driven-development (4 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 59 tokens to every session and 4,540 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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