The Derry spreadsheet that converts every euro invoice by hand is now load-bearing, and only one person understands it
Internal tools for a Derry firm typically cost $25k to $80k over 6 to 16 weeks, depending on how many processes you're replacing. You build custom when Retool, Airtable and spreadsheets have quietly become the operating system for your cross-border work, and a key process now depends on one person's hand-built workbook that nobody else can safely touch.
Every growing Derry firm reaches the point where the real business logic lives in spreadsheets. The currency-conversion workbook that turns euro invoices into sterling for the accounts. The tracker that flags which jobs crossed the border and need customs paperwork. The Airtable base someone built to manage device batches. Each one works until the person who built it is on holiday, or until two people edit it at once and the version that survives is the wrong one.
Retool gets you further, but it ties every internal tool to a subscription and a query model that struggles the moment your logic gets genuinely cross-border. When the rule is 'apply the settlement rate from the bank statement, not the booking rate, but only for ROI customers above a threshold', you've outgrown what a low-code wrapper around a spreadsheet can safely express.
The problems nobody warns you about
- A hand-built currency-conversion spreadsheet that's now business-critical and understood by exactly one person
- Airtable bases with no validation, so a mistyped VAT number or wrong currency silently corrupts downstream reports
- Cross-border job tracking split across tools that don't talk, so customs deadlines get missed
- Retool subscription costs climbing as every new internal process becomes another seat and another app
The case for owning your internal tools
Custom internal tools turn that fragile spreadsheet logic into something with validation, an audit trail and proper access control. The currency conversion that one person hand-runs becomes a tool anyone on the finance team can use safely, with the settlement-rate rule enforced rather than remembered. For a Derry firm where the cross-border process is the business, owning those tools means the knowledge stops living in one head and one workbook.
Budgeting a internal tools build in Derry
| Project scope | Typical cost | Timeline |
|---|---|---|
| Single high-value tool (e.g. cross-border conversion) | $25k to $40k | 6 to 8 weeks |
| Suite replacing several spreadsheets and Airtable bases | $50k to $80k | 10 to 16 weeks |
| Pilot tool to prove value before committing | $12k to $20k | 3 to 4 weeks |
What your build should include
What we build under internal tools in Derry
Everything a internal tools build here can cover:
Exactly what you get
You get the fragile parts of your operation turned solid. The currency-conversion workbook becomes a tool the whole finance team can run, with the settlement-rate rule enforced. The customs tracker alerts you before a deadline instead of after. Data entry rejects bad input at source. And the tools read live from your CRM, ERP and inventory management software, so nobody is working from a stale export.
How to choose a developer in Derry
Choose a team that starts by mapping which of your spreadsheets are genuinely load-bearing and which are just convenient, then builds the one that pays back fastest. The North West values practical, no-nonsense delivery, so favour a developer who'll ship a useful tool in weeks over one selling a grand platform. Ask to see an internal tool they built that replaced a critical spreadsheet, and what broke before they did.
- !They want to rebuild everything as custom from day one. Ask which single tool would pay back fastest and start there
- !No mention of validation or audit trail. Ask how the tool prevents a wrong currency or VAT number being entered
- !They propose another Retool app with no plan for the complex cross-border rules. Ask how the settlement-rate rule is enforced
- !They don't ask which spreadsheets are load-bearing. Ask them to map your critical processes before quoting
- !No integration plan, so the tool becomes another island. Ask how it reads live data from your CRM and ERP
Teams investing in internal tools in Derry usually scope it next to custom software, wordpress, accounting, since these systems share data and budgets.
Rohan advises mid-market and enterprise teams on ERP, CRM and custom software, and has led delivery on dozens of business-software builds.
Writes for Digital Heroes, shipping business software for 2,000+ brands across 55+ countries since 2017.
Frequently asked questions
When is a spreadsheet genuinely fine and when isn't it?
A spreadsheet is fine when the process is simple, low-stakes and only one person uses it. It stops being fine when it's business-critical, several people touch it, or a typo reaches a customer. In Derry the classic tipping point is the cross-border currency-conversion workbook that's quietly become essential.
Can't we just move everything into Retool or Airtable?
For straightforward processes, yes. But cross-border logic like 'apply the bank settlement rate, not the booking rate, for ROI customers above a threshold' is where low-code gets brittle and expensive. At that point a custom tool with proper validation is more reliable and often cheaper over time.
How much does a single internal tool cost?
A single high-value tool, like a cross-border conversion engine, runs $25k to $40k over 6 to 8 weeks. A suite replacing several spreadsheets and Airtable bases runs $50k to $80k over 10 to 16 weeks. A pilot to prove value first can be done for $12k to $20k.
What if the person who built our spreadsheet leaves?
That's exactly the risk custom tools remove. The logic moves out of one person's head and one workbook into a maintained system with documentation, validation and access control, so the business no longer has a single point of failure.